Heat-conductive silicone composition

ABSTRACT

A heat-conductive silicone composition comprising at least (A) an organopolysiloxane, (B) a heat-conductive filler, and (C) a specific organosiloxane. The silicone composition is excellent in handleability, even when it contains a large amount of a heat-conductive filler for the purpose of attaining higher heat conductivity.

The present invention relates to a thermally conductive siliconecomposition, and more specifically, to a thermally conductive siliconecomposition exhibiting excellent handleability despite containing alarge quantity of thermally conductive fillers added to produce asilicone composition exhibiting high thermal conductivity.

BACKGROUND ART

In recent years, following an increase in the degree of density andintegration of hybrid ICs and printed circuit boards that carrytransistors, ICs, memory elements, and other electronic components,various thermally conductive silicone compositions have been used inorder to achieve efficient heat release from such devices. Publiclyknown thermally conductive silicone compositions include thermallyconductive silicone greases, thermally conductive silicone gelcompositions, and thermally conductive silicone rubber compositions.

Examples of thermally conductive silicone compositions that have beenproposed include, for instance, a thermally conductive siliconecomposition comprising a vinyl-containing organosiloxane, anorganohydrogenpolysiloxane, a thermally conductive filler, an adhesionpromoter selected from aminosilane, epoxysilane, or alkyl titanate, anda platinum catalyst (see Japanese Unexamined Patent ApplicationPublication No. Sho 61-157569), a thermally conductive siliconecomposition comprising an organosiloxane containing an average of twoalkenyl groups per molecule, an organosiloxane containing an average ofthree or more silicon-bonded hydrogen atoms per molecule, a thermallyconductive filler made up of zinc oxide and magnesium oxide, a fillertreating agent, and a platinum catalyst (see Japanese Unexamined PatentApplication Publication No. Sho 62-184058), a thermally conductivesilicone composition comprising an organosiloxane containing at least0.1 mol % alkenyl groups per molecule, an organohydrogenpolysiloxanecontaining at least two silicon-bonded hydrogen atoms per molecule, aspherical alumina powder with an average particle size of 10 to 50 μm, aspherical or non-spherical alumina powder with an average particle sizeof less than 10 μm, and platinum or a platinum compound (see JapaneseUnexamined Patent Application Publication No.63-251466), a thermallyconductive silicone composition comprising an alkenyl-containingorganosiloxane, an organohydrogenpolysiloxane, an irregular-shapedalumina powder with an average particle size of 0.1 to 5 μm, a sphericalalumina powder with an average particle size of 5 to 50 μm, and aplatinum catalyst (see Japanese Unexamined Patent ApplicationPublication No. Hei 2-41362), a thermally conductive siliconecomposition comprising an organosiloxane containing at least twosilicon-bonded alkenyl groups per molecule, anorganohydrogenpolysiloxane containing at least three silicon-bondedhydrogen atoms per molecule, a thermally conductive filler with anaverage particle size of 5 to 20 μm, an adhesion promoter, and platinumor a platinum compound (see Japanese Unexamined Patent ApplicationPublication No. Hei 2-97559).

To increase the thermal conductivity of such thermally conductivesilicone compositions, the content of the thermally conductive fillersin the compositions has to be increased. This, however, brings aboutproblems in terms of the handleability and moldability of the resultantsilicone compositions.

In addition, other examples of thermally conductive siliconecompositions that have been proposed include, for instance, a thermallyconductive silicone composition comprising an organosiloxane containingat least two silicone-bonded alkenyl groups per molecule, anorganohydrogenpolysiloxane containing at least two silicon-bondedhydrogen atoms per molecule, an organosiloxane containing at least onesilicon-bonded alkoxy group or silicon-bonded hydroxyl group permolecule, a spherical or non-spherical alumina micropowder with anaverage particle size of less than 10 μm, a spherical or non-sphericalalumina micropowder with an average particle size of 10 to 50 μm, and ahydrosilation reaction catalyst (Japanese Unexamined Patent ApplicationPublication No. Hei 8-325457), a thermally conductive siliconecomposition comprising liquid silicone, at least one thickener selectedfrom zinc oxide, alumina, aluminum nitride, boron nitride, or siliconcarbide, an organosiloxane having at least one hydroxyl group directlybonded to a silicon atom per molecule, and an alkoxysilane (JapaneseUnexamined Patent Application Publication No. Hei 11-49958).

However, in such thermally conductive silicone compositions, theorganosiloxane containing at least one silicon-bonded hydroxyl group permolecule is substantially a diorganosiloxane having both terminal endsof its molecular chain blocked by silanol groups. When the amount of thethermally conductive fillers in the composition is increased in order toimprove the thermal conductivity of the cured silicone product obtainedby curing such a diorganosiloxane, the handleability and moldability ofthe resultant silicone composition deteriorates.

Furthermore, Japanese Unexamined Patent Application Publication No.2000-256558 and Japanese Unexamined Patent Application Publication No.2001-139815 have suggested using a dimethylpolysiloxane represented bythe formula:

(where x is an integer of 5 to 100) in thermally conductive siliconecompositions.

However, when such a thermally conductive silicone composition is loadedwith high levels of alumina or a similar thermally conductive fillers inorder to improve the thermal conductivity of the cured silicone productobtained by curing such a composition, the viscosity of the resultantcomposition rapidly increases and its handleability and moldabilitymarkedly deteriorate.

As a result of in-depth investigations into the above-describedproblems, the present inventors arrived at the present invention.

Namely, it is an object of the present invention to provide a thermallyconductive silicone composition exhibiting excellent handleabilitydespite containing a large quantity of thermally conductive fillersadded to obtain a silicone composition exhibiting high thermalconductivity.

DISCLOSURE OF INVENTION

The thermally conductive silicone composition of the present inventionis characterized by comprising:

(A) an organopolysiloxane,

(B) a thermally conductive filler, and

(C) at least one organosiloxane selected from the group consisting of

-   -   (i) an organosiloxane represented by the general formula:        {R¹ _(a)R² _((3−a))SiO(R¹ _(b)R² _((2−b))SiO)_(m)(R²        ₂SiO)_(n)}cSiR2_({4−(c+d)})(OR³)_(d)    -    where R¹ is monovalent hydrocarbon groups having aliphatic        unsaturated bonds, R² is identical or different monovalent        hydrocarbon groups without aliphatic unsaturated bonds, R³ is an        alkyl, alkoxyalkyl, alkenyl, or acyl, the subscript a is an        integer of 0 to 3, b is 1 or 2, c is an integer of 1 to 3, d is        an integer of 1 to 3, c+d is an integer of 2 to 4, m is an        integer of 0 or greater, and n is integer of 0 or greater, with        the proviso that m is an integer of 1 or greater when a is 0,    -   (ii) an organosiloxane having one silicon-bonded hydroxyl group        and at least five silicon atoms per molecule,    -   (iii) an organosiloxane represented by the general formula:

-   -    where R⁴ is identical or different monovalent hydrocarbon        groups, R⁵ is an oxygen atom or divalent hydrocarbon group, R³        is the same as defined above, p is an integer of 100 to 200, and        d is the same as above, and    -   (iv) an organosiloxane represented by the general formula:        {H_(e)R² _((3−e))SiO(R² ₂SiO)_(n)}SiR² _({4−(c+d)})(OR³)_(d)    -    where R², R³, c, d, and n are the same as defined above, and e        is an integer of 1 to 3.

DETAILED DESCRIPTION OF THE INVENTION

The thermally conductive silicone composition of the present inventionwill be now explained in detail.

The present composition is characterized by comprising at least theabove-mentioned Component (A), Component (B), and Component (C). Inaddition, the present composition can be rendered curable when it isfurther combined with (D) a curing agent. In such a case, there are nolimitations concerning the cure mechanism of the present composition,which can be based, for instance, on a hydrosilation reaction,condensation reaction, or an organic peroxide-induced free radicalreaction. The hydrosilation reaction is preferable because thecomposition cures faster and does not generate by-products.

The organopolysiloxane of Component (A) is the main component of thepresent composition. Methyl, ethyl, propyl, butyl, pentyl, hexyl,heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl,pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, andother linear alkyl groups; isopropyl, tertiary butyl, isobutyl, 2-methylundecyl, 1-hexylheptyl, and other branched allkyl groups; cyclopentyl,cyclohexyl, cyclododecyl, and other cyclic alkyl groups; vinyl, allyl,butenyl, pentenyl, hexenyl, and other alkenyl groups; phenyl, tolyl,xylyl, and other aryl groups; benzyl, phenetyl,2-(2,4,6-trimethylphenyl)propyl, and other aralkyl groups;3,3,3-trifluoropropyl, 3-chloropropyl, and other halogenated alkylgroups are suggested as the silicon-bonded groups of theorganopolysiloxane. Preferably, such groups are alkyl, alkenyl, or arylgroups, and especially preferably, methyl, vinyl, or phenyl. Inaddition, there are no limitations on the viscosity of theorganopolysiloxane at 25° C. However, the viscosity is preferably withinthe range of from 20 to 100,000 mPa·s, more preferably, within the rangeof from 50 to 100,000 mPa·s, still more preferably, within the range offrom 50 to 50,000 mPa·s, and especially preferably, within the range offrom 100 to 50,000 mPa·s. This is due to the fact that when itsviscosity at 25° C. is less than the lower limit of the above-mentionedrange, the physical properties of the resultant silicone compositionstend to markedly decrease, and, on the other hand, when it exceeds theupper limit of the above-mentioned range, the handleability of theresultant silicone compositions tends to decrease. There are nolimitations concerning the molecular structure of such anorganopolysiloxane, which may be, for instance, linear, branched,partially branched linear, or dendritic (dendrimeric), and is preferablylinear or partially branched linear. Examples of suchorganopolysiloxanes include, for instance, homopolymers possessing theabove-mentioned molecular structures, copolymers having theabove-mentioned molecular structures, or mixtures of the above-mentionedpolymers.

Dimethylpolysiloxane having both terminal ends of its molecular chainblocked by dimethylvinylsiloxy groups, dimethylpolysiloxane having bothterminal ends of its molecular chain blocked by methylphenylvinylsiloxygroups, dimethylsiloxane-methylphenyl siloxane copolymer having bothterminal ends of its molecular chain blocked by dimethylvinylsiloxygroups, dimethylsiloxane-methylvinylsiloxane copolymer having bothterminal ends of its molecular chain blocked by dimethylvinylsiloxygroups, dimethylsiloxane-methylvinylsiloxane copolymer having bothterminal ends of its molecular chain blocked by trimethylsiloxy groups,methyl(3,3,3-trifluoropropyl)-polysiloxane having both terminal ends ofits molecular chain blocked by dimethyl-vinylsiloxy groups,dimethylsiloxane-methylvinylsiloxane copolymer having both terminal endsof its molecular chain blocked by silanol groups,dimethylsiloxane-methylvinyl-siloxane-methylphenylsiloxane copolymerhaving both terminal ends of its molecular chain blocked by silanolgroups, organosiloxane copolymer consisting of siloxane unitsrepresented by the formula (CH₃)₃SiO_(1/2), siloxane units representedby the formula (CH₃)₂(CH₂═CH)SiO_(1/2), siloxane units represented bythe formula CH₃SiO_(3/2), and siloxane units represented by the formula(CH₃)₂SiO_(2/2), dimethylpolysiloxane having both terminal ends of itsmolecular chain blocked by silanol groups, dimethylsiloxane-methylphenylsiloxane copolymer having both terminal ends of its molecular chainblocked by silanol groups, dimethylpolysiloxane having both terminalends of its molecular chain blocked by trimethoxysiloxy groups,dimethylsiloxane-methylphenylsiloxane copolymer having both terminalends of its molecular chain blocked by trimethoxysilyl groups,dimethylpolysiloxane having both terminal ends of its molecular chainblocked by methyldimethoxysiloxy groups, dimethylpolysiloxane havingboth terminal ends of its molecular chain blocked by triethoxysiloxygroups, dimethylpolysiloxane having both terminal ends of its molecularchain blocked by trimethoxysilylethyl groups, and mixtures of two ormore of the above-mentioned compounds are suggested as examples of suchorganopolysiloxanes.

In addition, when the present composition is cured by means of ahydrosilation reaction, Component (A) is preferably anorganopolysiloxane having an average of not less than 0.1 silicon-bondedalkenyl groups per molecule. More preferably, it is anorganopolysiloxane having an average of not less than 0.5 silicon-bondedalkenyl groups per molecule, and especially preferably, it is anorganopolysiloxane having an average of not less than 0.8 silicon-bondedalkenyl groups per molecule. This is due to the fact that when theaverage number of silicon-bonded alkenyl groups per molecule is lessthan the lower limit of the above-mentioned range, the resultantcompositions tend to fail to cure to a sufficient extent. Thesilicon-bonded alkenyl groups of the organopolysiloxane are exemplifiedby the same alkenyl groups as those mentioned above and are preferablyrepresented by vinyl. In addition, silicon-bonded groups other than thealkenyl groups in the organopolysiloxane are exemplified by the samelinear alkyl, branched alkyl, cyclic alkyl, aryl, aralkyl, halogenatedalkyl groups as those mentioned above. They are preferably representedby alkyl and aryl groups, and especially preferably, by methyl andphenyl. In addition, although there are no limitations concerning theviscosity of the organopolysiloxane at 25° C., its viscosity ispreferably within the range of from 20 to 100,000 mPa·s, morepreferably, within the range of from 50 to 100,000 mPa·s, still morepreferably, within the range of from 50 to 50,000 mPa·s, and especiallypreferably, within the range of from 100 to 50,000 mPa·s. This is due tothe fact that when the viscosity of the composition at 25° C. is lessthan the lower limit of the above-mentioned range, the physicalproperties of the resultant cured silicone products tend to markedlydeteriorate, and, on the other hand, when it exceeds the upper limit ofthe above-mentioned range, the handleability of the resultant siliconecompositions tends to deteriorate. There are no limitations concerningthe molecular structure of such organopolysiloxanes, which isexamplified by the same structures as those mentioned above, and ispreferably linear or linear with partial branching. Suchorganopolysiloxanes are exemplified, for instance, by homopolymershaving the above-mentioned molecular structures, copolymers having theabove-mentioned molecular structures, or mixtures of these polymers.Such organopolysiloxanes are exemplified by organopolysiloxanes havingthe same alkenyl groups as those mentioned above.

In addition, when the present composition is cured by means of acondensation reaction, Component (A) is an organopolysiloxane having atleast two silanol groups or silicon-bonded hydrolyzable groups permolecule. Examples of the silicon-bonded hydrolyzable groups in theorganopolysiloxane include, for instance, methoxy, ethoxy, propoxy, andother alkoxy groups; vinyloxy, propenoxy, isopropenoxy,1-ethyl-2-methylvinyloxy, and other alkenoxy groups; methoxyethoxy,ethoxyethoxy, methoxypropoxy, and other alkoxyalkoxy groups; acetoxy,octanoyloxy, and other acyloxy groups; dimethylketoxime,methylethylketoxime, and other ketoxime groups; dimethylamino,diethylamino, butylamino, and other amino groups; dimethylaminoxy,diethylaminoxy, and other aminoxy groups; N-methylacetamido groups,N-ethylacetamido, and other amido groups. In addition, the silanolgroups and silicon-bonded hydrolyzable groups of the organopolysiloxaneare exemplified by the same linear alkyl, branched alkyl, cyclic alkyl,alkenyl, aryl, aralkyl, and halogenated alkyl groups as those mentionedabove. In addition, although there are no limitations concerning theviscosity of the organopolysiloxane at 25° C., its viscosity ispreferably in the range of from 20 to 100,000 mPa·s, more preferably, inthe range of from 50 to 100,000 mPa·s, and especially preferably, in therange of from 100 to 100,000 mPa·s. This is due to the fact that whenits viscosity at 25° C. is less than the lower limit of theabove-mentioned range, the physical properties of the resultant curedsilicone products tend to undergo marked deterioration, and, on theother hand, when it exceeds the upper limit of the above-mentionedrange, the handleability of the resultant silicone compositions tends toconspicuously deteriorate. There are no limitations concerning themolecular structure of such organopolysiloxanes, which is exemplified bythe same structures as those mentioned above and is preferably linear orpartially branched linear. Such organopolysiloxanes are exemplified byorganopolysiloxanes having at least two silanol groups or silicon-bondedhydrolyzable groups per molecule, said groups being the same as thosementioned above.

In addition, when the present composition is cured by means of anorganic peroxide-induced free radical reaction, there are no limitationsconcerning the organopolysiloxane of Component (A). However, it ispreferably an organopolysiloxane having at least one silicon-bondedalkenyl group. Silicon-bonded groups in such an organopolysiloxane areexamplified by the same linear alkyl, branched alkyl, cyclic alkyl,alkenyl, aryl, aralkyl, and halogenated alkyl groups as those mentionedabove and are preferably alkyl, alkenyl, or aryl groups, with methyl,vinyl, and phenyl being particularly preferable. In addition, althoughthere are no limitations concerning the viscosity of theorganopolysiloxane at 25° C., it is preferably in the range of from 20to 100,000 mPa·s, more preferably, in the range of from 50 to 100,000mPa·s, still more preferably, in the range of from 50 to 50,000 mPa·s,and especially preferably, in the range of from 100 to 50,000 mPa·s.This is due to the fact that when its viscosity at 25° C. is less thanthe lower limit of the above-mentioned range, the physical properties ofthe resultant cured silicone products tend to conspicuously deteriorate,and, on the other hand, when it exceeds the upper limit of theabove-mentioned range, the handleability of the resultant siliconecompositions is subject to conspicuous deterioration. There are nolimitations concerning the molecular structure of such anorganopolysiloxane, which is exemplified by the same structures as thosementioned above and is preferably linear or partially branched linear.Such organopolysiloxanes are exemplified, for instance, by homopolymershaving the above-mentioned molecular structures, copolymers having theabove-mentioned molecular structures, or mixtures of the above-mentionedpolymers. Such organopolysiloxanes are exemplified by the sameorganopolysiloxanes as those mentioned above.

The thermally conductive filler of Component (B) is a component used toimpart thermal conductivity to the resultant silicone composition andcan be, for instance, aluminum powder, copper powder, nickel powder, orother metal powders; alumina powder, magnesia powder, beryllia powder,chromia powder, titania powder, or other metal oxide powders; boronnitride powder, aluminum nitride powder, or other metal nitride powders;born carbide powder, titanium carbide powder, silicon carbide powder, orother metal carbide powders; powders of Fe—Si alloys, Fe—Al alloys,Fe—Si—Al alloys, Fe—Si—Cr alloys, Fe—Ni alloys, Fe—Ni—Co alloys,Fe—Ni—Mo alloys, Fe—Co alloys, Fe—Si—Al—Cr alloys, Fe—Si—B alloys,Fe—Si—Co—B alloys; and other soft magnetic alloy powders; Mn—Zn ferrite,Mn—Mg—Zn ferrite, Mg—Cu—Zn ferrite, Ni—Zn ferrite, Ni—Cu—Zn ferrite,Cu—Zn ferrite, or other ferrites, and mixtures of two or more of theabove-mentioned materials in addition, the shape of Component (B) canbe, for instance, spherical, acicular, disk-like, rod-like, oblate, orirregular. When electrical insulation properties are required of thepresent composition, or the resultant cured silicone product obtained bycuring the present composition, Component (B) is preferably a metaloxide powder, metal nitride powder, or metal carbide powder, especiallypreferably, an alumina powder. There are no limitations concerning theaverage particle size of Component (B), which is preferably in the rangeof from 0.1 to 100 μm, and especially preferably, in the range of from0.1 to 50 μm. In addition, when alumina powder is used as the thermallyconductive filler of Component (B), it is preferably a mixture of (B₁) aspherical alumina powder with an average particle size greater than 5 to50 μm and (B₂) a spherical or irregular-shaped alumina powder with anaverage particle size of 0.1 to 5 μm. Furthermore, in such a mixture,the content of the above-mentioned component (B₁) is preferably in therange of from 30 to 90 wt % and the content of the above-mentionedcomponent (B₂) is preferably in the range of from 10 to 70 wt %.

In the present composition, there are no limitations concerning thecontent of Component (B). However, in order to form a siliconecomposition of excellent thermal conductivity, its content in thepresent composition in vol % should preferably be at least 30 vol %,more preferably, in the range of from 30 to 90 vol %, still morepreferably, in the range of from 60 to 90 vol %, and especiallypreferably, in the range of from 80 to 90 vol %. In the same manner, inorder to form a silicone composition of excellent thermal conductivity,the content of Component (B) in wt % in the present composition shouldpreferably be at least 50 wt %, more preferably, in the range of from 70to 98 wt %, and especially preferably, in the range of from 90 to 97 wt%. Specifically, the content of Component (B) is preferably in the rangeof from 500 to 2,500 parts by weight, more preferably, in the range offrom 500 to 2,000 parts by weight, and especially preferably, in therange of from 800 to 2,000 parts by weight per 100 parts by weight ofComponent (A). This is due to the fact that when the content ofComponent (B) is less than the lower limit of the above-mentioned range,the thermal conductivity of the resultant silicone compositions tends tobe insufficient, and, on the other hand, when it exceeds the upper limitof the above-mentioned range, the viscosity of the resultant siliconecompositions becomes too high and it becomes impossible to uniformlydisperse Component (B) in the resultant silicone compositions and theirhandleability tends to conspicuously deteriorate.

Component (C) is a characteristic component used to obtain a thermallyconductive silicone composition exhibiting excellent handleabilitydespite containing a large quantity of the above-mentioned thermallyconductive fillers of Component (B) used to produce a siliconecomposition exhibiting high thermal conductivity, and is at least oneorganosiloxane selected from the group consisting of (i) organosiloxanerepresented by the general formula:{R¹ _(a)R² _((3−a))SiO(R¹ _(b)R² _((2−b))SiO)_(m)(R² ₂SiO)_(n)}_(c)SiR²_({4−(c+d)})(OR³)_(d)where R¹ stand for monovalent hydrocarbon groups having aliphaticunsaturated bonds, R² stand for identical or different monovalenthydrocarbon groups having no aliphatic unsaturated bonds, R³ is analkyl, alkoxyalkyl, alkenyl, or acyl, the subscript a is an integer of 0to 3, b is 1 or 2, c is an integer of 1 to 3, d is an integer of 1 to 3,c+d is an interger of 2 to 4, m is an integer of 0 or greater, and n isinteger of 0 or greater, with the proviso that m is an integer of 1 orgreater when a is 0, (ii) an organosiloxane having one silicon-bondedhydroxyl group and at least five silicon atoms per molecule, (iii) anorganosiloxane represented by the general formula:

where R⁴ stand for identical or different monovalent hydrocarbon groups,R⁵ is an oxygen atom or divalent hydrocarbon group, R³ is the same asdefined above, p is an integer of 100 to 200, and d is the same asabove, and (iv) an organosiloxane represented by the general formula:{H_(e)R² _((3−e))SiO(R² ₂SiO)_(n)}_(c)SIR² _({4−(c+d)})(OR³)_(d)where R², R³, c, d, and n are the same as defined above, and e is aninteger of 1 to 3.

Component (i) is used to prevent the handleability and moldability ofthe present composition from deteriorating when a large quantity of thethermally conductive fillers of Component (B) are added in order toobtain a silicone composition exhibiting high thermal conductivity aswell as to impart it with excellent adhesive properties with respect tothe substrates the present composition comes in contact with in theprocess of curing if it is curable, and is represented by the generalformula:{R¹ _(a)R² _((3−a))SiO(R¹ _(b)R² _((2−b))SiO)_(m)(R² ₂SiO)_(n)}_(c)SiR²_({4−(c+d)})(OR³)_(d)In the formula above, R¹ is monovalent hydrocarbon groups havingaliphatic unsaturated bonds, for instance, vinyl, allyl, butenyl,hexenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecyl,pentadecenyl, hexadecyl, heptadecenyl, octadecenyl, nonadecenyl,eicosenyl, and other linear alkenyl groups; isopropenyl,2-methyl-2-propenyl, 2-methyl-10-undecenyl, and other branched alkenylgroups; vinylcyclohexyl, vinylcyclododecyl, and other cyclic alkylgroups having aliphatic unsaturated bonds; vinylphenyl, and other arylgroups having aliphatic unsaturated bonds; vinylbenzyl, vinylphenetyl,and other aralkyl groups having aliphatic unsaturated bond. Preferably,these groups are linear alkenyl groups, and especially preferably,vinyl, allyl, or hexenyl. There are no limitations concerning theposition of the aliphatic unsaturated bonds in R¹, but it is preferablya position located far from the attached silicon atoms. In addition, R²in the formula above stand for identical or different monovalenthydrocarbon groups that have no aliphatic unsaturated bonds, exemplifiedby the same linear alkyl, branched alkyl, cyclic alkyl, aryl, aralkyl,and halogenated alkyl groups as those mentioned above, preferably, byalkyl or aryl groups, and even more preferably, by C_(1 to 4) alkylgroups, and especially preferably, by methyl or ethyl. In addition, R³in the formula above stands for alkyl, alkoxyalkyl, alkenyl, or acylgroups. The alkyl groups of R³ are exemplified, for instance, by thesame linear alkyl, branched alkyl, and cyclic alkyl groups as thosementioned above, preferably, by linear alkyl groups, and especiallypreferably, by methyl, ethyl, or propyl. In addition, the groupssuggested as the alkoxy groups of R³ are, for instance, methoxyethoxy,ethoxyethoxy, or methoxypropoxy, with methoxyethoxy being preferable. Inaddition, the alkenyl groups of R³, are exemplified by the same alkenylgroups as those shown above, preferably by isopropenyl. In addition, theacyl groups of R³ include, for instance, the acetoxy group. In addition,the subscript <<a>> in the formula above is an integer of 0 to 3,preferably 1. In addition, subscript b in the formula above is 1 or 2,preferably 1. In addition, the subscript c in the formula above is aninteger of 1 to 3, preferably 1. In addition, the subscript d in theformula above is an integer of 1 to 3, preferably 3. The sum c+d in theformula above is an integer of 2 to 4. In addition, m in the formulaabove is an integer of 0 or greater. However, when the above-mentionedsubscript a is 0, m is an integer of 1 or greater. The subscript m ispreferably an integer of 0 to 100, more preferably, an integer of 1 to100, still more preferably, an integer of 1 to 50, even more preferably,an integer of 1 to 25, and especially preferably, an integer of 1 to 10.In addition, the subscript <<n>> in the formula above is an integer of 0or greater. The subscript n is preferably an integer of 0 to 100, morepreferably, an integer of 1 to 100, still more preferably, an integer of5 to 100, even more preferably, an integer of 10 to 100, and especiallypreferably, an integer of 10 to 75.

As for the methods used to prepare the organosiloxane of Component (i),for instance, a method can be suggested, in which an organosiloxaneblocked by a silanol group at one of the ends of its molecular chain,represented by the general formula:{R¹ _(a)R² _((3−a))SiO(R¹ _(b)R² _((2−b))SiO)_(m)(R² ₂SiO)_(n)}H,and a silane compound represented by the general formula:R² _((4−f))Si(OR³)_(f)are reacted in the presence of acetic acid or another acid catalyst. Inthe above-mentioned silanol-capped organosiloxane, the R¹ and R² in theformula are the same groups as those mentioned above. In addition, thesubscripts a, b, m, and n are the same integers as those mentionedabove. On the other hand, in the above-mentioned silane compound, R² andR³ in the formula are the same groups as those mentioned above. Inaddition, the subscript <<f>> in the formula is an integer of 2 to 4,preferably 4. Examples of such silane compounds include, for instance,dimethoxydimethylsilane, dimethoxydiethylsilane, diethoxydimethylsilane,diethoxydiethylsilane, and other dialkoxydialkylsilanes;trimethoxymethylsilane, trimethoxyethylsilane, trimethoxypropylsilane,triethoxymethylsilane, triethoxyethylsilane, and othertrialkoxyalkylsilanes; tetramethoxysilane, tetraethoxysilane,tetrapropoxysilane, and other tetraalkoxysilanes;methyltri(methoxyethoxy)silane, and other alkoxyalkoxysilanes;methyltriisopropenoxy-silane, and other alkenoxysilanes;methyltriacetoxysilane, and other acyloxysilanes. In addition, examplesof the acid catalysts include, for instance, acetic acid, propionicacid, and other fatty acids.

The organosiloxanes of Component (i) are exemplified by the followingcompounds.

-   (CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₅Si(OCH₃)₃-   (CH₂═CHCH₂)(CH₃)₂SiO{(CH₃)₂SiO}₅Si(OCH₃)₃-   (CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO{(CH₃)₂SiO}₅Si(OCH₃)₃-   (CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₇Si(OCH₃)₃-   (CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₇Si(OC₂H₅)₃-   (CH₂═CHCH₂)(CH₃)₂SiO{(CH₃)₂SiO}₇Si(OCH₃)₃-   (CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO{(CH₃)₂SiO}₇Si(OCH₃)₃-   (CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₇SiCH₃(OCH₃)₂-   (CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₇SiCH₃(OCH₃)₂-   (CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₂₅Si(OCH₃)₃-   (CH₂═CHCH₂)(CH₃)₂SiO{(CH₃)₂SiO}₂₅Si(OCH₃)₃-   (CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO{(CH₃)₂SiO}₂₅Si(OCH₃)₃-   (CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₂₅Si(OC₂H₅)₃-   (CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₂₅SiCH₃(OCH₃)₂-   (CH₂═CH)(CH₃)₂SiO {(CH₃)₂SiO}₅₀Si(OCH₃)₃-   (CH₂═CHCH₂)(CH₃)₂SiO{(CH₃)₂SiO}₅₀Si(OCH₃)₃-   (CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO{(CH₃)₂SiO}₅₀Si(OCH₃)₃-   (CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₅₀Si(OC₂H₅)₃-   (CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₅₀SiCH₃(OCH₃)₂-   {(CH₃)₃SiO{(CH₂═CH)(CH₃)SiO}₁{(CH₃)₂SiO}₄}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CH)₂SiO}₁{(CH₃)₂SiO}₄}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CH)(CH₃)SiO}₁{(CH₃)₂SiO}₄}Si(OC₂H₅)₃-   {(CH₂═CH)(CH₃)₂SiO{(CH₂═CH)(CH₃)SiO}₁{(CH₃)₂SiO}₄}Si(OCH₃)₃-   {(CH₂═CH)(CH₃)₂SiO{(CH₂═CH)₂SiO}₁{(CH₃)₂SiO}₄}Si(OCH₃)₃-   {(CH₂═CH)(CH₃)₂SiO{(CH₂═CH)(CH₃)SiO}₁{(CH₃)₂SiO}₄}Si(OC₂H₅)₃-   {(CH₃)₃SiO{(CH₂═CHCH₂)(CH₃)SiO}₁{(CH₃)₂SiO}₄}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CHCH₂)₂SiO)₁{(CH₃)₂SiO}₄}Si(OCH₃)₃-   {(CH₂═CHCH₂)(CH₃)₂SiO{(CH₂═CH)(CH₃)SiO}₁{(CH₃)₂SiO}₄}Si(OHC₃)₃-   {(CH₂═CHCH₂)(CH₃)₂SiO{(CH₂═CHCH₂)(CH₃)SiO}₁{(CH₃)₂SiO}₄}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)SiO}₁{(CH₃)₂SiO}₄}Si(OCH₃)₃-   {(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO{(CH₂═CH)(CH₃)SiO}₁{(CH₃)₂SiO}₄}Si(OCH₃)₃-   {(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO{(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)SiO}₁{(CH₃)₂SiO}₄}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CH)(CH₃)SiO}₂{(CH₃)₂SiO}₁₀}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CH)₂SiO}₂{(CH₃)₂SiO}₁₀}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CH)(CH₃)SiO}₂{(CH₃)₂SiO}₁₀}Si(OC₂H₅)₃-   {(CH₂═CH)(CH₃)₂SiO{(CH₂═CH)(CH₃)SiO}₂{(CH₃)₂SiO}₁₀}Si(OCH₃)₃-   {(CH₂═CH)(CH₃)₂SiO{(CH₂═CH)₂SiO}₂{(CH₃)₂SiO}₁₀}Si(OCH₃)₃-   {(CH₂═CH)(CH₃)₂SiO {(CH₂═CH)(CH₃)SiO}₂{(CH₃)₂SiO}₁₀}Si(OC₂H₅)₃-   {(CH₃)₃SiO{(CH₂═CHCH₂)(CH₃)SiO}₂{(CH₃)₂SiO}₁₀}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CHCH₂)₂SiO}₂{(CH₃)₂SiO}₁₀}Si(OCH₃)₃-   {(CH₂═CHCH₂)(CH₃)₂SiO{(CH₂═CH)(CH₃)SiO)₂{(CH₃)₂SiO)}₁₀}Si(OCH₃)₃-   {(CH₂═CHCH₂)(CH₃)₂SiO{(CH₂═CHCH₂)(CH₃)SiO}₂{(CH₃)₂SiO}₁₀}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)SiO}₂{(CH₃)₂SiO}₁₀}Si(OCH₃)₃-   {(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO{(CH₂═CH)(CH₃)SiO}₂{(CH₃)₂SiO}₁₀}Si(OCH₃)₃-   {(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO{(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)SiO}₂}(CH₃)₂SiO}₁₀}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CH)(CH₃)SiO}₃{(CH₃)₂SiO}₂₂}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CH)₂SiO}₃{(CH₃)₂SiO}₂₂}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CH)(CH₃)SiO}₃{(CH₃)₂SiO}₂₂}Si(OC₂H₅)₃-   {(CH₂═CH)(CH₃)₂SiO{(CH₂═CH)(CH₃)SiO}₃{(CH₃)₂SiO}₂₂}Si(OCH₃)₃-   {(CH₂═CH)(CH₃)₂SiO{(CH₂═CH)₂SiO}₃{(CH₃)₂SiO}₂₂}Si(OCH₃)₃-   {(CH₂═CH)(CH₃)₂SiO{(CH₂═CH)(CH₃)SiO}₃{(CH₃)₂SiO}₂₂}Si(OC₂H₅)₃-   {(CH₃)₃SiO{(CH₂═CHCH₂)(CH₃)SiO}₃{(CH₃)₂SiO}₂₂}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CHCH₂)₂SiO}₃{(CH₃)₂SiO}₂₂}Si(OCH₃)₃-   {(CH₂═CHCH₂)(CH₃)₂SiO{(CH₂═CH)(CH₃)SiO}₃{(CH₃)₂SiO}₂₂}Si(OCH₃)₃-   {(CH₂═CHCH₂)(CH₃)₂SiO{(CH₂═CHCH₂)(CH₃)SiO}₃{(CH₃)₂SiO}₂₂}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)SiO}₃{(CH₃)₂SiO}₂₂}Si(OCH₃)₃-   {(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO{(CH₂═CH)(CH₃)SiO}₃{(CH₃)₂SiO}₂₂}Si(OCH₃)₃-   {(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO{(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)SiO}₃{(CH₃)₂SiO}₂₂}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CH)(CH₃)SiO}₄{(CH₃)₂SiO}₅₀}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CH)₂SiO}₄{(CH₃)₂SiO}₅₀}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CH)(CH₃)SiO}₄{(CH₃)₂SiO}₅₀}Si(OC₂H₅)₃-   {(CH₂═CH)(CH₃)₂SiO{(CH₂═CH)(CH₃)SiO}₄{(CH₃)₂SiO}₅₀}Si(OCH₃)₃-   {(CH₂═CH)(CH₃)₂SiO{(CH₂═CH)₂SiO}₄{(CH₃)₂SiO}₅₀}Si(OCH₃)₃-   {(CH₂═CH)(CH₃)₂SiO{(CH₂═CH)(CH₃)SiO}₄{(CH₃)₂SiO}₅₀}Si(OC₂H₅)₃-   {(CH₃)₃SiO{(CH₂═CHCH₂)(CH₃)SiO}₄{(CH₃)₂SiO}₅₀}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CHCH₂)₂SiO}₄{(CH₃)₂SiO}₅₀}Si(OCH₃)₃-   {(CH₂═CHCH₂)(CH₃)₂SiO{(CH₂═CH)(CH₃)SiO}₄{(CH₃)₂SiO}₅₀}Si(OCH₃)₃-   {(CH₂═CHCH₂)(CH₃)₂SiO{(CH₂═CHCH₂)(CH₃)SiO}₄{(CH₃)₂SiO}₅₀}Si(OCH₃)₃-   {(CH₃)₃SiO{(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)SiO}₄{(CH₃)₂SiO}₅₀}Si(OCH₃)₃-   {(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO{(CH₂═CH)(CH₃)SiO)}₄{(CH₃)₂SiO}₅₀}Si(OCH₃)₃-   {(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO{(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)SiO}₄{(CH₃)₂SiO}₅₀}Si(OCH₃)₃

Component (ii), which is an organosiloxane having one silicon-bondedhydroxyl group and at least five silicon atoms per molecule, imparts thepresent composition with characteristics allowing it to have excellenthandleability despite containing a large quantity of the thermallyconductive filler of Component (B), which is added in order to obtain asilicone composition exhibiting high thermal conductivity. It is belivedthat Component (ii) acts as a plasticizer or treating agent that treatsthe surface of the thermally conductive filler of component (B) via thesilicon-bonded hydroxyl groups, thereby lowering the viscosity of theresultant composition and enabling addition of even higher amounts ofthe fillers.

In addition, Component (ii) needs to have only one silicon-bondedhydroxyl group per molecule. A number of 2 or more promotes bondingbetween the particles of Component (B), which renders the viscosity ofthe resultant composition excessively high and makes it impossible toachieve higher levels of loading. In addition, per molecule, Component(ii) needs to have at least five silicon atoms, preferably, at least 10atoms, even more preferably, 10 to 500 atoms, and especially preferably,50 to 200 atoms. This is due to the fact that organosiloxane in whichthe number of silicon atoms per molecule is less than the lower limit ofthe above-mentioned range have molecules of excessively small size, andit tends to be impossible to treat the surface of Component (B) to asufficient extent, and, in addition, in organosiloxanes in which itexceeds the upper limit of the above-mentioned range, the molecularvolume bound by the surface of Component (B) increases excessively andit becomes difficult to increase the level of loading of Component (B).

There are no limitations concerning the organosiloxane of Component(ii), examples of which include, for instance,

Component (ii) is preferably an organosiloxane represented by thegeneral formula:

R⁴ in the formula above are identical or different monovalenthydrocarbon groups exemplified by the same linear alkyl, branched alkyl,cyclic alkyl, aryl, aralkyl, alkenyl, and halogenated alkyl groups asthose mentioned above. Preferably, these are alkyl groups, andespecially preferably, methyl. In addition, the subscript <<r>> in theformula above is an integer of 5 or greater, preferably, an integer of10 to 500, and especially preferably, an integer of 50 to 200.

In addition, the organosiloxane of Component (iii) is a component whichis characterized by being capable of producing a thermally conductivesilicone composition exhibiting excellent handleability even if itcontains large quanitites of the above-described thermally conductivefiller of Component (B), which is added in order to produce a siliconecomposition exhibiting high thermal conductivity. This is due to thefact that in the organosiloxane, which has a silicon-bonded hydrolyzablegroup at one of the ends of its molecular chain, diorganosiloxane repeatunits are within a specified range. This organosiloxane is representedby the general formula:

Where R⁴ are identical or different monovalent hydrocarbon groupsexemplified by the same linear alkyl, branched alkyl, cyclic alkyl,aryl, aralkyl, alkenyl, and halogenated alkyl groups as those mentionedabove, preferably by linear alkyl groups, and especially preferably, bymethyl. In addition, R⁵ in the formula is an oxygen atom or a divalenthydrocarbon group. The divalent hydrocarbon groups of R⁵ include, forinstance, methylene, ethylene, propylene, isopropylene, butylene, andother alkylene groups; ethylenoxyethylene, ethylenoxypropylene, andother alkylenoxyalkylene groups. Particularly preferably, R⁵ is anoxygen atom. In addition, R³ in the formula above is represented by thesame groups as those mentioned above. In addition, the subscript <<p>>is an integer of 100 to 200, preferably, an integer of 105 to 200, morepreferably, an integer of 105 to 190, and especially preferably, aninteger of 110 to 190. This is due to the fact that when the subscript<<p>> in the formula above is less than the lower limit of theabove-mentioned range, addition of large quanitities of Component (B) inorder to obtain a thermally conductive silicone composition tends tobecome imposssible, and, on the other hand, when it exceeds the upperlimit of the above-mentioned range, the molecular volume bound by thesurface of Component (B) increases excessively, and addition of a largequantity of Component (B) tends to become impossible. In particular, ifthe content of Component (B) in the present composition is madeextremely high, such as 80 vol % or more, this trend becomes moreconspicuous because the average distance between the particles ofComponent (B) become shorter. In addition, the subscript <<d>> is aninteger of 1 to 3, preferably 3.

Examples of the organosiloxane of Component (iii) include, for instance,

In addition, the organosiloxane of Component (iv) is used to prevent thehandleability of the present composition from deteriorating when a largequantity of the thermally conductive fillers of Component (B) are addedin order to obtain a silicone composition exhibiting high thermalconductivity as well as to impart it with superior moldability andexcellent adhesive properties with respect to the substrates it comes incontact with in the process of curing if it is curable, and isrepresented by the general formula:{H_(e)R² _((3−e))SiO(R² ₂SiO)_(n)}_(c)SIR² _({4−(c+d)})(OR³)_(d)In the formula above, R² are identical or different monovalenthydrocarbon groups having no aliphatic unsaturated bonds and exemplifiedby the same groups as those mentioned above, preferably, by alkyl oraryl groups, more preferably, by C_(1 to 4) alkyl groups, and especiallypreferably, by methyl or ethyl. In addition, R³ in the formula abovestands for alkyl, alkoxyalkyl, alkenyl, or acyl groups exemplified bythe same groups as those mentioned above, preferably alkyl groups, andespecially preferably, by methyl, ethyl, or propyl. In addition, thesubscript <<e>> is an integer of 1 to 3, preferably 1. In addition, thesubscript <<c>> in the formula above is an integer of 1 to 3,preferably 1. In addition, the subscript <<d>> in the formula above isan integer of 1 to 3, preferably 3. Also, the sum <<c+d>> in the formulaabove is an integer of 2 to 4. In addition, the subscript <<n>> is aninteger of 0 or greater, preferably, an integer of 0 to 100, morepreferably, an integer of 1 to 100, even more preferably, an integer of5 to 100, still more preferably, an integer of 10 to 100, and especiallypreferably, an integer of 10 to 75.

The methods used for the preparation of the organosiloxane of Component(iv) include, for instance, a process, in which an organosiloxane cappedwith a silanol group at one of the ends of its molecular chain,represented by the general formula:{H_(e)R² _((3−e))SiO(R² ₂SiO)_(n)}Hand a silane compound represented by the general formula:R² _((4−f))Si(OR³)_(f)are reacted in the presence of acetic acid or another acid catalyst. Inthe above-mentioned silanol-capped organosiloxane, R² are identical ordifferent monovalent hydrocarbon groups having no aliphatic unsaturatedbonds and exemplified by the same groups as those mentioned above. Inaddition, the subscript <<e>> in the formula above is an integer of 1 to3, preferably 1. In addition, the subscript n in the formula above is aninteger of 0 or greater, preferably an integer of 0 to 100, morepreferably, an integer of 1 to 100, still more preferably, an integer of5 to 100, even more preferably, an integer of 10 to 100, and especiallypreferably, an integer of 10 to 75. On the other hand, in theabove-mentioned silane compound, R² in the formula stand for identicalor different monovalent hydrocarbon groups having no aliphaticunsaturated bonds and exemplified by the same groups as those mentionedabove. In addition, R³ in the formula above stands for alkyl,alkoxyalkyl, alkenyl, or acyl groups exemplified by the same groups asthose mentioned above. In addition, the subscript <<f>> is an integer of2 to 4, preferably 4. Suggested silane compounds include, for instance,dimethoxydimethylsilane, dimethoxydiethylsilane, diethoxydimethylsilane,diethoxydiethylsilane, and other dialkoxydialkylsilanes;trimethoxymethylsilane, trimethoxyethylsilane, trimethoxypropylsilane,triethoxymethylsilane, triethoxyethylsilane, and othertrialkoxyalkylsilanes; tetramethoxysilane, tetraethoxysilane,tetrapropoxysilane, and other tetraalkoxysilanes;methyltri(methoxyethoxy)silane, and other alkoxyalkoxysilanes;methyltriisopropenoxysilane, and other alkenoxysilanes;methyltriacetoxysilane, and other acyloxysilanes. In addition, suggestedacid catalysts include, for instance, acetic acid, propionic acid, andother fatty acids.

The organosiloxane of Component (iv) is exemplified by the followingcompounds.

-   H(CH₃)₂SiO{(CH₃)₂SiO}₅Si(OCH₃)₃-   H(CH₃)₂SiO{(CH₃)₂SiO}₅Si(OC₂H₅)₃-   H(C₂H₅)₂SiO{(CH₃)₂SiO}₅Si(OCH₃)₃-   H(C₆H₁₃)₂SiO{(CH₃)₂SiO}₅Si(OCH₃)₃-   H(CH₃)₂SiO{(CH₃)₂SiO}₁₀Si(OCH₃)₃-   H(CH₃)₂SiO{(CH₃)₂SiO}₂₅Si(OCH₃)₃-   H(CH₃)₂SiO{(CH₃)₂SiO}₂₅Si(OC₂H₅)₃-   H(C₂H₅)₂SiO{(CH₃)₂SiO}₂₅Si(OCH₃)₃-   H(CH₃)(C₂H₅)SiO{(CH₃)₂SiO}₂₅Si(OCH₃)₃-   H(C₆H₁₃)₂SiO{(CH₃)₂SiO}₂₅Si(OCH₃)₃-   H(CH₃)₂SiO{(CH₃)₂SiO}₅₀Si(OCH₃)₃-   H(CH₃)₂SiO{(CH₃)₂SiO}₅₀Si(OC₂H₅)₃-   H(C₂H₅)₂SiO{(CH₃)₂SiO}₅₀Si(OCH₃)₃-   H(CH₃)₂SiO{(CH₃)₂SiO}₇₅Si(OCH₃)₃-   H(CH₃)₂SiO{(CH₃)₂SiO}₁₀₀Si(OCH₃)₃-   H(CH₃)(C₂H₅)SiO{(CH₃)₂SiO}₁₀₀Si(OCH₃)₃-   H(C₂H₅)₂SiO{(CH₃)₂SiO}₁₀₀Si(OC₂H₅)₃-   H(C₆H₁₃)₂SiO{(CH₃)₂SiO}₁₀₀Si(OCH₃)₃-   H(CH₃)₂SiO{(CH₃)₂SiO}₁₂₀Si(OCH₃)₃

In the present composition, there are no limitations concerning thecontent of Component (C). The content should permit sufficient treatmentof the surface of Component (B) to improve its dispersibility in theresultant thermally conductive silicone composition. Specifically, thecontent should be preferably in the range of from 0.1 to 10 parts byweight per 100 parts by weight of Component (B), and especiallypreferably, in the range of from 0.1 to 5 parts by weight per 100 partsby weight of Component (B). This is due to the fact that when thecontent of Component (C) is less than the lower limit of theabove-mentioned range, adding a large quantity of Component (B) leads toa decrease in the moldability of the resultant silicone composition andComponent (B) tends to precipitate and separate during the storage ofthe resultant silicone composition. On the other hand, when it exceedsthe upper limit of the above-mentioned range, the physical properties ofthe resultant silicone composition tend to deteriorate.

In addition, in the present composition, any single component or acombination of two or more of the above-mentioned Component (i) throughComponent (iv) can be used as the above-mentioned Component (C). Inaddition, in order to obtain a thermally conductive silicone compositionexhibiting excellent handleability even if it contains a large quantityof the thermally conductive filler of Component (B) added with a view toobtain a silicone composition exhibiting high thermal conductivity, asilane compound represented by the general formula:R⁴ _((4−g))Si(OR³)_(g)(where R⁴ stands for a monovalent hydrocarbon group, R³ stands for analkyl, alkoxyalkyl, alkenyl, or acyl group, and the subscript <<g>> isan integer of 1 to 3), or an organosiloxane represented by the generalformula:

where R⁴ stands for identical or different monovalent hydrocarbongroups, R⁵ stands for an oxygen atom or divalent hydrocarbon group, R³stands for an alkyl, alkoxy alkyl, alkenyl, or acyl group, the subscripty is an integer of 0 to 99, and the subscript d is an integer of 1 to 3can be used in combination with the above-mentioned Component (C).

In the silane compound, R⁴ in the formula stands for a monovalenthydrocarbon group exemplified by the same groups as those mentionedabove. In addition, R³ in the formula stands for an alkyl, alkoxyalkyl,alkenyl, or acyl group exemplified by the same groups as those mentionedabove. In addition, the subscript g in the formula is an integer of 1 to3, preferably 2 or 3. Such silane compounds are exemplified bymethyltrimethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane,octyltrimethoxysilane, nonyltrimethoxysilane, decyltrimethoxysilane,vinyltrimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane,and other alkoxysilanes; methyltri(methoxyethoxy)silane, and otheralkoxyalkoxysilane; methyltriisopropenoxysilane, and otheralkenoxysilanes; methyltriacetoxysilane, and other acyloxysilanes.

In addition, in this organosiloxane, R⁴ in the formula stand foridentical or different monovalent hydrocarbon groups exemplified by thesame groups as those mentioned above. In addition, R⁵ in the formulastands for an oxygen atom or divalent hydrocarbon group exemplified bythe same groups as those mentioned above. In addition, R³ in the formulastands for an alkyl, alkoxyalkyl, alkenyl, or acyl group exemplified bythe same groups as those mentioned above. In addition, the subscript yis an integer of 0 to 99, preferably, an integer of 0 to 80, andespecially preferably, an integer of 0 to 60. In addition, the subscriptd in the formula is an integer of 1 to 3, preferably 3. Suchorganosiloxanes are exemplified, for instance, by

In the present composition, there are no limitations concerning thecontent of the above-mentioned silane compound or organosiloxane. Thecontent should be sufficient to treat the surface of the above-describedComponent (B) with Component (C) so as to improve its dispersibility inthe resultant thermally conductive silicone composition, specifically,it is preferably in the range of from 0.001 to 10 parts by weight per100 parts by weight of Component (B), and especially preferably, in therange of from 0.001 to 5 parts by weight per 100 parts by weight ofComponent (B). This is due to the fact that when the content of theabove-mentioned silane compound or organosiloxane is less than the lowerlimit of the above-mentioned range, addition of large quanitities ofComponent (B) leads to a decrease in the moldability of the resultantsilicone composition as well as to the precipitation and separation ofComponent (B) during storage of the resultant silicone composition andto a marked drop in its consistency. On the other hand, when it exceedsthe upper limit of the above-mentioned range, the physical properties ofthe resultant silicone composition tend to conspicuously deteriorate.

The methods used to add Component (C), or Component (C) and theabove-mentioned silane compound or organosiloxane to the presentcomposition include, for instance, a method of addition, in whichComponent (B) and Component (C), and, if needed, the above-mentionedsilane compound or organosiloxane as well, are mixed so as to treat thesurface of Component (B) first, or a method of addition, in whichComponent (A) and Component (B) are mixed and then combined withComponent (C), and, if needed, with the above-mentioned silane compoundor organosiloxane so as to treat the surface of Comonent (B) inComponent (A), with the latter method being particularly preferable.Thus, Component (C), or Component (C) and the above-mentioned silanecompound or organosiloxane, may be introduced into the presentcomposition in a state, in which the surface of Component (B) has beenalready treated, or introduced into the present composition separately.In addition, when Component (B) is treated with Component (C), or withComponent (C) and the above-mentioned silane compound or organosiloxane,to accelerate the treatment, it can be conducted under heating or incombination with acidic substances such as acetic acid, phosphoric acidetc., or basic substances such as trialkylamine, quaternary ammoniumsalts, ammonia gas, ammonium carbonate, etc.

The present composition may be further combined with (D) a curing agent,which makes it possible to produce a curable composition. When thepresent composition is cured by means of a hydrosilation reaction, thecuring agent of Component (D) is made up of a platinum catalyst and anorganopolysiloxane having an average of at least 2 silicon-bondedhydrogen atoms per molecule. The groups bonded to silicon atoms in theorganopolysiloxane are exemplified by the same linear alkyl, branchedalkyl, cyclic alkyl, aryl, aralkyl, and halogenated alkyl groups asthose mentioned above, preferably, by alkyl or aryl groups, andespecially preferably, by methyl or phenyl. In addition, although thereare no limitations concerning the viscosity of the organopolysiloxane at25° C., it is preferably in the range of from 1 to 100,000 mPa·s, andespecially preferably, in the range of from 1 to 5,000 mPa·s. There areno limitations concerning the molecular structure of suchorganopolysiloxanes. For instance, the structure can be linear,branched, partially branched linear, cyclic, or dendritic (dendrimeric).Suggested organopolysiloxanes include, for instance, homopolymers havingthe above-mentioned molecular structures, copolymers having theabove-mentioned molecular structures, or mixtures of such polymers.

Suggested organopolysiloxanes include, for instance,dimethylpolysiloxane having both terminal ends of its molecular chainblocked by dimethylhydrogensiloxy groups,dimethylsiloxane-methylhydrogensiloxane copolymer having both terminalends of its molecular chain blocked by trimethylsiloxy groups,dimethylsiloxane-methylhydrogensiloxane copolymer having both terminalends of its molecular chain blocked by dimethylhydrogensiloxy groups,organosiloxane copolymer consisting of siloxane units of the formula:(CH₃)₃ SiO_(1/2), siloxane units of the formula: (CH₃)₂ HSiO_(1/2), andsiloxane units of the formula: SiO_(4/2), and mixtures of two or more ofthe above-mentioned compounds.

In the present composition, the content of the organopolysiloxane is thecontent necessary to cure the present composition. Specifically, it ispreferably sufficient to provide between 0.1 mol and 10 mol, morepreferably, between 0.1 mol and 5 mol, and especially preferably,between 0.1 mol to 3.0 mol of silicon-bonded hydrogen atoms from thecomponent per 1 mol of silicon-bonded alkenyl groups of Component (A).This is due to the fact that when the content of this component is lessthan the lower limit of the above-mentioned range, the resultantsilicone composition tends to fail to completely cure, and, on the otherhand, when it exceeds the upper limit of the above-mentioned range, theresultant cured silicone product is extremely hard and tends to developnumerous cracks on the surface.

In addition, the platinum catalyst is a catalyst used to promote thecuring of the present composition. Suggested examples of such catalystsinclude, for instance, chloroplatinic acid, alcohol solutions ofchloroplatinic acid, olefin complexes of platinum, alkenylsiloxanecomplexes of platinum, and carbonyl complexes of platinum.

In the present composition, the content of platinum catalyst is thecontent necessary for curing the present composition. Specifically, itis sufficient to provide, in weight units, preferably between 0.01 ppmand 1,000 ppm, and particularly preferably between 0.1 ppm and 500 ppmof platinum metal from the component relative to the amount of Component(A). This is due to the fact that when the content of the component isless than the lower limit of the above-mentioned range, the resultantsilicone composition tends to fail to completely cure, and, on the otherhand, adding an amount exceeding the upper limit of the above-mentionedrange does not significantly improve the cure rate of the the resultantsilicone composition.

In addition, when the present composition is cured by means of acondensation reaction, Component (D) is characterized by consisting of asilane having at least 3 silicon-bonded hydrolyzable groups per moleculeor a partial hydrolyzate thereof, and, if needed, a condensationreaction catalyst. The silicon-bonded hydrolyzable groups in the silaneare exemplified by the same alkoxy, alkoxyalkoxy, acyloxy, ketoxime,alkenyl, amino, aminoxy, and amido groups as those mentioned above. Inaddition to the above-mentioned hydrolyzable groups, examples of groupsthat can be bonded to the silicon atoms of the silane include, forinstance, the same linear alkyl, branched alkyl, cyclic alkyl, alkenyl,aryl, aralkyl, and halogenated alkyl groups as those mentioned above.Suggested silanes or their partial hydrolyzates include, for instance,methyltriethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, andethyl orthosilicate.

In the present composition, the content of the silane or its partialhydrolyzate is the content necessary to cure the present composition.Specifically, it is preferably in the range of from 0.01 to 20 parts byweight, and especially preferably, in the range of from 0.1 to 10 partsby weight per 100 parts by weight of Component (A). This is due to thefact that when the content of the silane or its partial hydrolyzate isless than the lower limit of the above-mentioned range, the storagestability of the resultant composition deteriorates, and, in addition,its adhesive properties tende to decrease. On the other hand, when itexceeds the upper limit of the above-mentioned range, the cure of theresultant composition tends to conspicuously slow down.

In addition, the condensation reaction catalyst is an optional componentwhich is not essential when using silanes having, for instance, aminoxy,amino, ketoxime, and other hydrolyzable groups as curing agents.Suggested condensation reaction catalysts include, for instance,tetrabutyl titanate, tetraisopropyl titanate, and other organictitanates; diisopropoxybis(acetylacetate)titanium,diisopropoxybis(ethylacetoacetate)titanium, and other chelateorganotitanium compounds; aluminum tris(acetylacetonate), aluminumtris(ethylacetoacetate), and other oranic aluminum compounds; zirconiumtetra(acetylacetonate), zirconium tetrabutyrate, and other oraniczirconium compounds; dibutyltin dioctoate, dibutyltin dilaurate,butyltin-2-ethylhexoate, and other organotin compounds; tinnaphthenoate, tin oleate, tin butyrate, cobalt naphthenoate, zincstearate, and other metal salts of organic carboxylic acids; hexylamine,dodecylamine phosphates and other amine compounds or their salts;benzyltriethylammonium acetate, and other quaternary ammonium salts;potassium acetate, lithium nitrate, and other lower fatty acid salts ofalkali metals; dimethylhydroxylamine, diethylhydroxylamine, and otherdialkylhydroxylamines; and guanidyl-containing organosilicon compounds.

In the present composition, the content of the condensation reactioncatalyst is arbitrary, and should be sufficient to cure the presentcomposition. Specifically, it is preferably in the range of from 0.01 to20 parts by weight, and especially preferably, in the range of from 0.1to 10 parts by weight per 100 parts by weight of Component (A). This isdue to the fact that if the catalyst is essential, then a catalystcontent smaller than the lower limit of the above-mentioned range tendsto make it difficult for the resultant composition to cure completely,and, on the other hand, when the content exceeds the upper limit of theabove-mentioned range, the storage stability of the resultantcomposition tends decrease.

In addition, when the present composition is cured by means of anorganic peroxide-induced free radical reaction, Component (D) is anorganic peroxide. Suggested organic peroxides include, for instance,benzoyl peroxide, dicumyl peroxide,2,5-dimethyl-bis(2,5-t-butylperoxy)hexane, di-t-butyl peroxide, andt-butylperbenzoate.

The content of the organic peroxides is the content necessary to curethe present composition, specifically, it is preferably in the range offrom 0.1 to 5 parts by weight per 100 parts by weight of theorganopolysiloxane of the above-mentioned Component (A).

Furthermore, so long as the object of the present invention is notimpaired, the present composition may contain other optional components,for instance, fumed silica, precipitated silica, fumed titania, andother fillers; fillers obtained by treating the surface of theabove-mentioned fillers with organosilicon compounds to render ithydrophobic; 3-glycidoxypropyltrimethoxysilane,3-methacryloxypropyltrimethoxysilane, and other adhesion promoters; and,additionally, pigments, dyes, fluorescent dyes, heat resistant agents,triazole compounds, and other flame retardants, and plasticizing agents.

In particular, when the present composition is cured by means of ahydrosilation reaction, to adjust the cure rate of the presentcomposition and improve its handleability, it is preferable to combineit with 2-methyl-3-butyn-2-ol, 2-phenyl-3-butyn-2-ol,1-ethynyl-1-cyclohexanol, and other acetylene compounds;3-methyl-3-penten-1-yne, 3,5-dimethyl-3-hexen-1-yne, and other ene-ynecompounds; and, in addition, hydrazine compounds, phosphine compounds,mercaptan compounds, and other cure reaction inhibitors. There are nolimitations concerning the content of the cure reaction inhibitors,however, preferably it is in the range of from 0.0001 to 1.0 wt %relative to the amount of the present composition.

In case the present composition is curable, there are no limitationsconcering the method of curing. The method, for instance, may involvemolding the present composition and then allowing it to stand at roomtemperature, or molding the present composition and then heating it to50 to 200° C. In addition, there are no limitations concerning thephysical characteristics of the thus obtained silicone, but suggestedforms include, for instance, gels, low-hardness rubbers, orhigh-hardness rubbers.

EXAMPLES

The thermally conductive silicone composition of the present inventionwill be now explained by referring to Practical Examples. Additionally,it should be noted that the physical characteristics described in thePractical Example s are represented by values obtained at 25° C.

Practical Example 1

To 84.7 parts by weight of dimethylpolysiloxane with a viscosity of 400mPa·s having both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups (vinyl group content=0.44 wt %) were added900 parts by weight of spherical alumina powder with an average particlesize of 10 μm, and 10 parts by weight of organosiloxane represented bythe formula:(CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₂₅Si(OCH₃)₃and combined in a mixer. Next, 4.3 parts by weight ofdimethylsiloxane-methylhydrogensiloxane copolymer having both terminalends of its molecular chain blocked by trimethylsiloxy groups, aviscosity of 5 mPa·s and an average of five silicon-bonded hydrogenatoms per molecule (content of silicon-bonded hydrogen atoms=0.74 wt %)and 0.5 parts by weight of 1-ethynyl-1-cyclohexanol as a cure reactioninhibitor were combined with the mixture. Finally, a thermallyconductive silicone rubber composition was prepared by combining themixture with 0.5 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt %.

The characteristics of the thermally conductive silicone rubbercomposition and thermally conductive silicone rubber were determined asfollows, with the results listed in Table 1.

Consistency Of Thermally Conductive Silicone Rubber Composition

The ¼ cone penetration consistency of the thermally conductive siliconerubber composition was measured in accordance with the method stipulatedin JIS K 2220. A high consistency value was interpreted as evidence ofthe high plasticity and superior handleability of the thermallyconductive silicone rubber composition.

Moldability Of Thermally Conductive Silicone Rubber Composition

A layer of the thermally conductive silicone rubber composition with athickness of 2 mm was produced by sandwiching it between pieces ofethylene tetrafluoride resin film with a thickness of 0.2 mm, afterwhich it was cured by heating at 150° C. for 15 minutes. After that, theethylene tetrafluoride resin film was peeled off and visual examinationwas carried out to determine whether a silicone rubber sheet had beenformed. When a uniform silicone rubber sheet was formed, the moldabilityof the composition was evaluated as “excellent” and designated as “∘”;when a sheet was formed, but had locations of partially low strength,the moldability was evaluated as “somewhat good” and designated as “□”;and when a sheet could not be formed, or had low strength when formed,the moldability was evaluated as “no good” and designated as “x”.

Thermal Conductivity Of Thermally Conductive Silicone Rubber

The thermal conductivity of the thermally conductive silicone rubberobtained by heating the thermally conductive silicone rubber compositionat 150° C. for 15 minutes was determined in accordance with the hot wiremethod stipulated in JIS R 2616 using a Quick Thermal ConductivityMeter, the QTM-500, manufactured by Kyoto Electronics Manufacturing Co.,Ltd.

Adhesive Strength Of Thermally Conductive Silicone Rubber

The thermally conductive silicone rubber composition was sandwichedbetween two pieces of identical material and then cured by heating at150° C. for 30 minutes. Aluminum plates (JIS H 4000, A1050P), nickelplates (SPCC-SB), and stainless steel plates (SUS-304 2B) from PaltekCo., Ltd. were used as the adherend material. In addition, the surfacearea of the plates, to which the composition was adhered, was 25 mm×10mm, and the thickness of the adhered layer was 1 mm. The tensile shearadhesive strength of the thermally conductive silicone rubber wasmeasured in accordance with JIS K 6249.

Practical Example 2

Dimethylpolysiloxane (85.4 parts by weight) with a viscosity of 400mPa·s having both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups (vinyl group content=0.44 wt %), 900 parts byweight of spherical alumina powder with an average particle size of 10μm, and 10 parts by weight of organosiloxane represented by the formula:(CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₅₀Si(OCH₃)₃were combined in a mixer. Next, 3.6 parts by weight ofdimethylsiloxane-methylhydrogensiloxane copolymer having both terminalends of its molecular chain blocked by trimethylsiloxy groups, aviscosity of 5 mPa·s, and an average of five silicon-bonded hydrogenatoms per molecule (content of silicon-bonded hydrogen atoms=0.74 wt %)and 0.5 parts by weight of 1-ethynyl-1-cyclohexanol as a cure reactioninhibitor were combined with the mixture. Finally, a thermallyconductive silicone rubber composition was prepared by combining themixture with 0.5 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt %. The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were determined in the same manner as in Practical Example 1, andthe results were listed in Table 1.

Practical Example 3

Dimethylpolysiloxane (83.7 parts by weight) with a viscosity of 400mPa·s having both terminal ends of its molecular chain blocked bydimethylvinyisiloxy groups (vinyl group content=0.44 wt %), 900 parts byweight of spherical alumina powder with an average particle size of 10μm, and 10 parts by weight of organosiloxane represented by the formula:{(CH₃)₃SiO{(CH₂═CH)(CH₃)SiO}_(2.7){(CH₃)₂SiO}₂₂}Si(OCH₃)₃were combined in a mixer. Next, 5.3 parts by weight ofdimethylsiloxane-methylhydrogensiloxane copolymer having both terminalends of its molecular chain blocked by trimethylsiloxy groups, aviscosity of 5 mPa·s, and an average of five silicon-bonded hydrogenatoms per molecule (content of silicon-bonded hydrogen atoms=0.74 wt %)and 0.5 parts by weight of 1-ethynyl-1-cyclohexanol as a cure reactioninhibitor were combined with the mixture. Finally, a thermallyconductive silicone rubber composition was prepared by combining themixture with 0.5 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt %. The physical properties of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were determined in the same manner as in Practical Example 1, andthe results were listed in Table 1.

Practical Example 4

Dimethylpolysiloxane (42.4 parts by weight) with a viscosity of 400mPa·s having both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups (vinyl group content=0.44 wt %), 552 parts byweight of spherical alumina powder with an average particle size of 40μm, 368 parts by weight of irregular-shaped alumina powder with anaverage particle size of 2.2 μm, and 30 parts by weight oforganosiloxane represented by the formula:{(CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₂₉}Si(OCH₃)₃were combined in a mixer. Next, 4.6 parts by weight ofdimethylsiloxane-methylhydrogensiloxane copolymer having both terminalends of its molecular chain blocked by trimethylsiloxy groups, aviscosity of 5 mPa·s, and an average of five silicon-bonded hydrogenatoms per molecule (content of silicon-bonded hydrogen atoms=0.74 wt %),0.5 parts by weight of 1-ethynyl-1-cyclohexanol as a cure reactioninhibitor, and 1.0 part by weight of 3-glycidoxypropyltrimethoxysilaneand 1.0 part by weight of dimethylsiloxane-methylvinylsiloxane copolymerhaving both terminal ends of its molecular chain blocked byhydroxydimethyl groups and an average of two silicon-bonded vinyl groupsper molecule (vinyl group content=9.6 wt %) as an adhesion promoter werecombined with the mixture. Finally, a thermally conductive siliconerubber composition was prepared by combining the mixture with 0.5 partsby weight of a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex ofplatinum with a platinum content of 0.5 wt %. The characteristics of thethermally conductive silicone rubber composition and thermallyconductive silicone rubber were determined in the same manner as inPractical Example 1, and the results were listed in Table 1.

Comparative Example 1

Dimethylpolysiloxane (85.4 parts by weight) with a viscosity of 400mPa·s having both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups (vinyl group content=0.44 wt %), 900 parts byweight of spherical alumina powder with an average particle size of 10μm, and 10 parts by weight of methyltrimethoxysilane were combined in amixer. Next, the mixture was combined with 3.6 parts by weight ofdimethylsiloxane-methylhydrogensiloxane copolymer having both terminalends of its molecular chain blocked by trimethylsiloxy groups, aviscosity of 5 mPa□s, and an average of five silicon-bonded hydrogenatoms per molecule (content of silicon-bonded hydrogen atoms=0.74 wt %)and 0.5 parts by weight of 1-ethynyl-1-cyclohexanol as a cure reactioninhibitor. Finally, a thermally conductive silicone rubber compositionwas prepared by combining the mixture with 0.5 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt %. The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were determined in the same manner as in Practical Example 1, andthe results were listed in Table 1.

Comparative Example 2

A thermally conductive silicone rubber composition was prepared in thesame manner as in Comparative Example 1 except for using an identicalamount of decyltrimethoxysilane instead of the methyltrimethoxysilaneused in Comparative Example 1. The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were determined in the same manner as in Practical Example 1 andthe results were listed in Table 1.

Comparative Example 3

A thermally conductive silicone rubber composition was prepared in thesame manner as in Comparative Example 1 except for using an identicalamount of organosiloxane represented by the formula:(CH₃)₃SiO{(CH₃)₂SiO}₅₀Si(OCH₃)₃instead of the methyltrimethoxysilane used in Comparative Example 1. Thecharacteristics of the thermally conductive silicone rubber compositionand thermally conductive silicone rubber were determined in the samemanner as in Practical Example 1 and the results were listed in Table 1.

TABLE 1 Examples Comparative Practical Examples Examples Parameters 1 23 4 1 2 3 Consistency (mm/10) 120 110 112 110 30 119 114 Moldability ◯ ◯◯ ◯ X X Δ Thermoconductivity 3.0 3.0 3.0 4.3 3.0 3.0 3.0 (W/mK) Adhesivestrength (N/cm²) Aluminum plates 372 275 349 301 212 54 13 Nickel plates293 262 295 — 193 60 22 Stainless steel plates 215 141 286 — 158 61 6.8

Practical Example 5

Dimethylpolysiloxane (100 parts by weight) with a viscosity of 400 mPa·shaving the ends of its molecular chain blocked by dimethylvinylsiloxygroups (vinyl group content=0.44 wt %), 1200 parts by weight of a truespherical alumina powder with an average particle size of 10 μm, 800parts by weight of an irregular-shaped alumina powder with an averageparticle size of 2.2 μm, and 20 parts by weight of dimethylsiloxanehaving one of the terminal ends of its molecular chain blocked by asilanol group, represented by the formula:

were mixed at room temperature for 30 minutes in a Ross mixer. Next, athermally conductive silicone rubber base was prepared by mixing 4.4parts by weight of dimethylpolysiloxane (content of silicon-bondedhydrogen atoms=0.12 wt %) with a viscosity of 10 mPa□s having bothterminal ends of its molecular chain blocked by dimethylhydrogensiloxygroups, 0.5 parts by weight of dimethylsiloxane-methylhydrogensiloxanecopolymer with a viscosity of 5 mPa□s having both terminal ends of itsmolecular chain blocked by trimethylsiloxy groups (content ofsilicon-bonded hydrogen atoms=0.64 wt %), and 0.02 parts by weight of2-phenyl-3-butyn-2-ol as a cure reaction inhibitor with the resultantmixture at room temperature for 15 minutes.

Some of the silicone rubber base was placed in a 50-ml glass beaker andthe ¼ cone penetration consistency of the silicone rubber base wasmeasured in accordance with the method stipulated in JIS K 2220, withthe results listed in Table 2. A high consistency value was interpretedas evidence of the high plasticity and superior handleability of thethermally conductive silicone rubber composition.

Next, a thermally conductive silicone rubber composition was prepared byuniformly mixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt %.

The characteristics of the thermally conductive silicone rubbercomposition and thermally conductive silicone rubber were measured asfollows, with the results listed in Table 2.

Moldability Of Thermally Conductive Silicone Rubber Composition

A layer of the thermally conductive silicone rubber composition with athickness of 1 mm was produced by sandwiching it betweeen pieces ofpolyethylene terephthalate resin film (PET film) with a thicknesss of 50μm, after which it was cured by heating at 100° C. for 30 minutes. Afterthat, the PET resin film was peeled off and visual examination wascarried out to determine whether a silicone rubber sheet had beenformed. When a uniform silicone rubber sheet was formed, the moldabilityof the composition was evaluated as “excellent” and designated as “∘”;when a sheet was formed, but had locations of partially low strength,the moldability was evaluated as “somewhat inferior” and designated as“□”; and when a sheet could not be formed, or had low strength whenformed, the moldability was evaluated as “no good” and designated as“x”.

Thermal Conductivity Of Thermally Conductive Silicone Rubber

The thermal conductivity of the thermally conductive silicone rubberobtained by heating the thermally conductive silicone rubber compositionat 100° C. for 30 minutes was determined in accordance with the hot wiremethod stipulated in JIS R 2616 using a Quick Thermal ConductivityMeter, the QTM-500, manufactured by Kyoto Electronics Manufacturing Co.,Ltd.

Hardness Of Thermally Conductive Silicone Rubber

The hardness of the thermally conductive silicone rubber obtained byheating the thermally conductive silicone rubber composition at 100° C.for 30 minutes was determined using a Type E durometer as stipulated inJIS K 6253.

Practical Example 6

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 5 except for using an identical amount ofdimethylsiloxane having one of the terminal ends of its molecular chainblocked by a silanol group, represented by the formula:

instead of the dimethylsiloxane having one of the terminal ends of itsmolecular chain blocked by a silanol group that was used in PracticalExample 5. The consistency of the thermally conductive silicone rubberbase was measured in the same manner as in Practical Example 5 and theresults were listed in Table 2.

Next, a thermally conductive silicone rubber composition was prepared byuniformly mixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt %. The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured in the same manner as in Practical Example 5 andthe results were listed in Table 2.

Practical Example 7

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 5 except for using an identical amount ofdimethylsiloxane having one of the terminal ends of its molecular chainblocked by a silanol group, represented by the formula:

instead of the dimethylsiloxane having one of the terminal ends of itsmolecular chain blocked by a silanol group that was used in PracticalExample 5. The consistency of the thermally conductive silicone rubberbase was measured in the same manner as in Practical Example 5 and theresults were listed in Table 2.

Next, a thermally conductive silicone rubber composition was prepared byuniformly mixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt %. The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured in the same manner as in Practical Example 5 andthe results were listed in Table 2.

Practical Example 8

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 5 except for using an identical amount ofdimethylsiloxane having one of the terminal ends of its molecular chainblocked by a silanol group, represented by the formula:

instead of the dimethylsiloxane having one of the terminal ends of itsmolecular chain blocked by a silanol group that was used in PracticalExample 5. The consistency of the thermally conductive silicone rubberbase was measured in the same manner as in Practical Example 5 and theresults were listed in Table 2.

Next, a thermally conductive silicone rubber composition was prepared byuniformly mixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt %. The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured in the same manner as in Practical Example 5 andthe results were listed in Table 2.

Comparative Example 4

100 parts by weight of dimethylpolysiloxane with a viscosity of 400mPa·s having both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups (vinyl group content=0.44 wt %), 1008 partsby weight of a true spherical alumina powder with an average particlesize of 10 m, and 672 parts by weight of an irregular-shaped aluminapowder with an average article size of 2.2 μm were mixed at roomtemperature for 30 minutes in a Ross mixer. Next, a thermally conductivesilicone rubber base was prepared by mixing 4.4 parts by weight ofdimethylpolysiloxane (content of silicon-bonded hydrogen atoms=0.12 wt%) with a viscosity of 10 mPa·s having both terminal ends of itsmolecular chain blocked by dimethylhydrogensiloxy groups, 0.5 parts byweight of dimethylsiloxane-methylhydrogensiloxane copolymer with aviscosity of 5 mPa·s having both terminal ends of its molecular chainblocked by trimethylsiloxy groups (content of silicon-bonded hydrogenatoms=0.64 wt %), and 0.02 parts by weight of 2-phenyl-3-butyn-2-ol as acure reaction inhibitor with the resultant mixture at room temperaturefor 15 minutes. The consistency of the thermally conductive siliconerubber base was measured in the same manner as in Practical Example 5and the results were listed in Table 2.

Next, a thermally conductive silicone rubber composition was prepared byuniformly mixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt %. The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured in the same manner as in Practical Example 5 andthe results were listed in Table 2. In comparison with PracticalExamples 5 through 8, its consistency prior to cure was high, and itshandleability was inferior. In addition to that, despite having the samecrosslinking density, it was found to have a higher post-cure hardness,which resulted in a loss of elasticity.

Comparative Example 5

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 5 except for using an identical amount ofdimethylsiloxane having both terminal ends of its molecular chainblocked by silanol groups, represented by the formula:

instead of the dimethylsiloxane having one of the terminal ends of itsmolecular chain blocked by a silanol group that was used in PracticalExample 5. However, the viscosity of the composition increasedexcessively, which made it impossible to add all of the 1,200 parts byweight of the true spherical alumina powder with an average particlesize of 10 μm and 800 parts by weight of the irregular-shaped aluminapowder with an average particle size of 2.2 μm. As a result, thedetermination of the consistency of the thermally conductive siliconerubber base, the evaluation of the moldability of the thermallyconductive silicone rubber composition, and the determination of thethermal conductivity and hardness of the thermally conductive siliconerubber could not be carried out.

Comparative Example 6

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 5 except for reducing the amount of thetrue spherical alumina powder with an average particle size of 10 μm to990 parts by weight and that of the irregular-shaped alumina powder withan average particle size of 2.2 μm to 660 parts by weight so as to bringtheir total content to 93 wt %. The consistency of the thermallyconductive silicone rubber base was measured in the same manner as inPractical Example 5 and the results were listed in Table 2.

Next, a thermally conductive silicone rubber composition was prepared byuniformly mixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt %. The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured in the same manner as in Practical Example 5 andthe results were listed in Table 2. In comparison with PracticalExamples 5 through 8, despite the fact that its thermal conductivity waslowered by reducing the loading levels of the true spherical aluminapowder with an average particle size of 10 μm and that of theirregular-shaped alumina powder with an average particle size of 2.2 μm,it was found to exhibit a high consistency prior to cure and poorhandleablity, and, in addtion to that, had a higher post-cure hardness,which resulted in a loss of elasticity.

Comparative Example 7

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 5 except for using an identical amount ofdimethylsiloxane having one of the terminal ends of its molecular chainblocked by a silanol group, represented by the formula:

instead of the dimethylsiloxane having one of the terminal ends of itsmolecular chain blocked by a silanol group that was used in PracticalExample 5. The consistency of the thermally conductive silicone rubberbase was measured in the same manner as in Practical Example 5 and theresults were listed in Table 2.

Next, a thermally conductive silicone rubber composition was prepared byuniformly mixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt %. The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured in the same manner as in Practical Example 5 andthe results were listed in Table 2. Although the dimethylsiloxane havingone of the terminal ends of its molecular chain blocked by a silanolgroup that was used in this example was identical to thedimethylsiloxane having one of the terminal ends of its molecular chainblocked by a silanol group that was used in Practical Examples 5 through8, because of the low degree of polymerization, efficient treatment wasimpossible and the resultant composition was found to exhibit a highconsistency prior to cure and poor handleablity, and, in addition tothat, had a higher post-cure hardness, which resulted in a loss ofelasticity.

TABLE 2 Example Comparative Practical Examples Examples Parameters 5 6 78 4 6 7 Consistency 55 58 63 80 33 15 29 (mm/10) Moldability ◯ ◯ ◯ ◯ Δ ΔΔ Thermal conductivity 4.8 4.6 4.6 4.6 4.7 4.0 4.5 (W/m · k) Hardness 4846 40 33 77 63 71

Practical Example 9

Dimethylpolysiloxane (100 parts by weight) with a viscosity of 400 mPa·shaving both ends of its molecular chain blocked by dimethylvinylsiloxygroups (vinyl group content=0.44 wt %), 1200 parts by weight of a truespherical alumina powder with an average particle size of 10 μm, 800parts by weight of an irregular-shaped alumina powder with an averageparticle size of 2.2 μm, and 20 parts by weight of dimethylsiloxanehaving one of the terminal ends of its molecular chain blocked by atrimethoxysiloxy group, represented by the formula:

were mixed at room temperature for 30 minutes in a Ross mixer, afterwhich a thermally conductive silicone rubber base was prepared by mixing4.4 parts by weight of dimethylpolysiloxane (content of silicon-bondedhydrogen atoms=0.12 wt %) with a viscosity of 10 mPa·s having bothterminal ends of its molecular chain blocked by dimethylhydrogensiloxygroups (an amount sufficient to provide 0.3 mol of silicon-bondedhydrogen atoms from the dimethylpolysiloxane per 1 mol of vinyl groupsfrom the above-mentioned dimethylpolysiloxane having both ends of itsmolecular chain blocked by dimethylvinylsiloxy groups), 0.5 parts byweight of dimethylsiloxane-methylhydrogensiloxane copolymer (content ofsilicon-bonded hydrogen atoms=0.64 wt %) with a viscosity of 5 mPa·shaving both terminal ends of its molecular chain blocked bytrimethylsiloxy groups (an amount sufficient to provide 0.2 mol ofsilicon-bonded hydrogen atoms from thedimethylsiloxane-methylhydrogensiloxane copolymer per 1 mol of vinylgroups from the above-mentioned dimethylpolysiloxane having both ends ofits molecular chain blocked by dimethylvinylsiloxy groups), and 0.02parts by weight of 2-phenyl-3-butyn-2-ol as a cure reaction inhibitor(an amount sufficient to provide a concentration of 0.001 wt % in thepresent composition) with the resultant mixture at room temperature for15 minutes.

Some of the silicone rubber base was placed in a 50-ml glass beaker andthe ¼ cone penetration consistency of the silicone rubber base wasmeasured in accordance with the method stipulated in JIS K 2220, withthe results listed in Table 3. A high consistency value was interpretedas evidence of the high plasticity and superior handleability of thethermally conductive silicone rubber composition.

Next, a thermally conductive silicone rubber composition was prepared byuniformly mixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt % (an amount sufficient to provide 10 ppm ofplatinum metal relative to the above-mentioned dimethylpolysiloxanehaving both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups). The content of alumina powder in thecomposition was 94.0 wt % (79.4 vol %). The characteristics of thethermally conductive silicone rubber composition and thermallyconductive silicone rubber were measured as follows and the results werelisted in Table 3.

Moldability Of Thermally Conductive Silicone Rubber Composition

A layer of the thermally conductive silicone rubber composition with athickness of 1 mm was produced by sandwiching it betweeen pieces ofpolyethylene terephthalate resin film (PET film) with a thicknesss of 50μm, after which it was cured by heating at 100° C. for 30 minutes. Afterthat, the PET resin film was peeled off and visual examination wascarried out to determine whether a silicone rubber sheet had beenformed. When a uniform silicone rubber sheet was successfully formed,the moldability of the composition was evaluated as “excellent” anddesignated as “∘”; when a sheet was formed, but exhibited partialcohesive failure, the moldability was evaluated as “somewhat inferior”and designated as “□”; and when a sheet could not be formed due tocohesive failure in a greater portion thereof, the moldability wasevaluated as “no good” and designated as “x”.

Thermal Conductivity Of Thermally Conductive Silicone Rubber

The thermal conductivity of the thermally conductive silicone rubberobtained by heating the thermally conductive silicone rubber compositionat 100° C. for 30 minutes was determined in accordance with the hot wiremethod stipulated in JIS R 2616 using a Quick Thermal ConductivityMeter, the QTM-500, manufactured by Kyoto Electronics Manufacturing Co.,Ltd.

Hardness Of Thermally Conductive Silicone Rubber

The hardness of the thermally conductive silicone rubber obtained byheating the thermally conductive silicone rubber composition at 100° C.for 30 minutes was determined using a Type E durometer as stipulated inJIS K 6253.

Practical Example 10

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 9 except for using an identical amount ofdimethylpolysiloxane having one of the terminal ends of its molecularchain blocked by a trimethoxysiloxy group, represented by the formula:

instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 9. The consistency of the silicone rubber base wasmeasured in the same manner as in Practical Example 9 and the resultswere listed in Table 3.

Next, a thermally conductive silicone rubber composition was prepared bymixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt % (an amount sufficient to provide 10 ppm ofplatinum metal relative to the above-mentioned dimethylpolysiloxanehaving both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups). The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured in the same manner as in Practical Example 9 andthe results were listed in Table 3.

Practical Example 11

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 9 except for using an identical amount ofdimethylpolysiloxane having one of the terminal ends of its molecularchain blocked by a trimethoxysiloxy group, represented by the formula:

instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 9. The consistency of the silicone rubber base wasmeasured in the same manner as in Practical Example 9 and the resultswere listed in Table 3.

Next, a thermally conductive silicone rubber composition was prepared bymixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt % (an amount sufficient to provide 10 ppm ofplatinum metal relative to the above-mentioned dimethylpolysiloxanehaving both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups). The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured in the same manner as in Practical Example 9 andthe results were listed in Table 3.

Comparative Example 8

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 9 except for using an identical amount ofdimethylpolysiloxane having one of the terminal ends of its molecularchain blocked by a trimethoxysiloxy group, represented by the formula:

instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 9. The consistency of the silicone rubber base wasmeasured in the same manner as in Practical Example 9 and the resultswere listed in Table 3.

Next, a thermally conductive silicone rubber composition was prepared bymixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt % (an amount sufficient to provide 10 ppm ofplatinum metal relative to the above-mentioned dimethylpolysiloxanehaving both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups). The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured in the same manner as in Practical Example 9 andthe results were listed in Table 3.

Comparative Example 9

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 9 except for using an identical amount ofdimethylpolysiloxane having one of the terminal ends of its molecularchain blocked by a trimethoxysiloxy group, represented by the formula:

instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 9. The consistency of the silicone rubber base wasmeasured in the same manner as in Practical Example 9 and the resultswere listed in Table 3.

Next, a thermally conductive silicone rubber composition was prepared bymixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt % (an amount sufficient to provide 10 ppm ofplatinum metal relative to the above-mentioned dimethylpolysiloxanehaving both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups). The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured in the same manner as in Practical Example 9 andthe results were listed in Table 3.

Comparative Example 10

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 9 except for using an identical amount ofdimethylpolysiloxane having one of the terminal ends of its molecularchain blocked by a trnethoxysiloxy group, represented by the formula:

instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 9. The consistency of the silicone rubber base wasmeasured in the same manner as in Practical Example 9 and the resultswere listed in Table 3.

Next, a thermally conductive silicone rubber composition was prepared bymixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt % (an amount sufficient to provide 10 ppm ofplatinum metal relative to the above-mentioned dimethylpolysiloxanehaving both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups). The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured in the same manner as in Practical Example 9 andthe results were listed in Table 3.

Comparative Example 11

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 9 except for using an identical amount ofdimethylpolysiloxane having one of the terminal ends of its molecularchain blocked by a trimethoxysiloxy group, represented by the formula:

instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 9. The consistency of the silicone rubber base wasmeasured in the same manner as in Practical Example 9 and the resultswere listed in Table 3.

Next, a thermally conductive silicone rubber composition was prepared bymixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt % (an amount sufficient to provide 10 ppm ofplatinum metal relative to the above-mentioned dimethylpolysiloxanehaving both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups). The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured in the same manner as in Practical Example 9 andthe results were listed in Table 3.

Comparative Example 12

An attempt was made to prepare a thermally conductive silicone rubberbase in the same manner as in Practical Example 9 except for using anidentical amount of dimethylpolysiloxane having both terminal ends ofits molecular chain blocked by trimethoxysiloxy groups, represented bythe formula:

instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 9, but an excessive increase in the viscosity of thebase made it impossible to add all of the 1,200 parts by weight of atrue spherical alumina powder with an average particle size of 10 μm andthe 800 parts by weight of an irregular-shaped alumina powder with anaverage particle size of 2.2 μm.

Comparative Example 13

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 9 except for using an identical amount ofdimethylpolysiloxane having both terminal ends of its molecular chainblocked by trimethoxysiloxy groups, represented by the formula:

instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 9. The consistency of the silicone rubber base wasmeasured in the same manner as in Practical, Example 9 and the resultswere listed in Table 3.

Next, a thermally conductive silicone rubber composition was prepared bymixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt % (an amount sufficient to provide 10 ppm ofplatinum metal relative to the above-mentioned dimethylpolysiloxanehaving both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups). The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured in the same manner as in Practical Example 9 andthe results were listed in Table 3.

TABLE 3 Examples Practical Examples Comparative Examples Parameters 9 1011 8 9 10 11 13 Consistency 95 94 92 38 58 65 75 28 (mm/10) Moldability◯ ◯ ◯ Δ ◯ ◯ ◯ Δ Thermal 4.5 4.6 4.6 4.8 4.7 4.6 4.6 4.8 conductivity(W/m · k) Hardness 22 24 26 72 50 40 37 84

In the thermally conductive silicone rubber compositions listed in Table3, the content of alumina powder was 79.4 vol %. Comparison betweenPractical Examples 9 through 11 and Comparative Examples 8 through 11showed that, depending on the number of dimethylsiloxane repeat units inthe dimethylpolysiloxanes having one of the terminal ends of theirmolecular chains blocked by trimethoxysiloxy groups, there wasconsiderable variation in the consistency of the thermally conductivesilicone rubber compositions, and, in addition, considerable variationin the hardness of the silicone rubbers obtained by curing them.Additionally, comparison between Practical Example 9 and ComparativeExample 13 showed that even if the number of dimethylsiloxane repeatunits in the dimethylpolysiloxanes was the same, the consistency of thethermally conductive silicone rubber composition greatly varied and, inaddition, there was considerable variation in the hardness of thesilicone rubber produced by curing the compositions depending on whetherthe molecular chain was blocked with a trimethoxysiloxy group at oneterminal end or with trimethoxysiloxy groups at both terminal ends.Furthermore, comparison between Comparative Example 12 and ComparativeExample 13 showed that when both terminal ends of the molecular chain ofthe dimethylpolysiloxane were blocked by trimethoxysiloxy groups, theconsistency of the thermally conductive silicone rubber compositionincreased and its handleability decreased regardless of the number ofdimethylsiloxane repeat units.

Practical Example 12

Dimethylpolysiloxane (100 parts by weight) with a viscosity of 400 mPa·shaving both ends of its molecular chain blocked by dimethylvinylsiloxygroups (vinyl group content=0.44 wt %), 1,500 parts by weight of a truespherical alumina powder with an average particle size of 10 μm, 1,000parts by weight of an irregular-shaped alumina powder with an averageparticle size of 2.2 μm, and 26 parts by weight of dimethylsiloxanehaving one of the terminal ends of its molecular chain blocked by atrimethoxysiloxy group, represented by the formula:

were mixed at room temperature for 30 minutes in a Ross mixer, afterwhich a thermally conductive silicone rubber base was prepared by mixing4.4 parts by weight of dimethylpolysiloxane (content of silicon-bondedhydrogen atoms=0.12 wt %) with a viscosity of 10 mPa·s having bothterminal ends of its molecular chain blocked by dimethylhydrogensiloxygroups (an amount sufficient to provide 0.3 mol of silicon-bondedhydrogen atoms from the dimethylpolysiloxane per 1 mol of vinyl groupsfrom the above-mentioned dimethylpolysiloxane having both ends of itsmolecular chain blocked by dimethylvinylsiloxy groups), 0.5 parts byweight of dimethylsiloxanemethylhydrogen-siloxane copolymer (content ofsilicon-bonded hydrogen atoms=0.64 wt %) with a viscosity of 5 mPa·shaving both terminal ends of its molecular chain blocked bytrimethylsiloxy groups (an amount sufficient to provide 0.2 mol ofsilicon-bonded hydrogen atoms from thedimethylsiloxane-methylhydrogensiloxane copolymer per 1 mol of vinylgroups from the above-mentioned dimethylpolysiloxane having both ends ofits molecular chain blocked by dimethylvinylsiloxy groups), and 0.02parts by weight of 2-phenyl-3-butyn-2-ol as a cure reaction inhibitor(an amount sufficient to provide a concentration of 0.001 wt % in thepresent composition) with the resultant mixture at room temperature for15 minutes. The consistency of the silicone rubber base was measured inthe same manner as in Practical Exmaple 9 and the results were listed inTable 4.

Next, a thermally conductive silicone rubber composition was prepared byuniformly mixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt % (an amount sufficient to provide 10 ppm ofplatinum metal relative to the above-mentioned dimethylpolysiloxanehaving both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups). The content of alumina powder in thecomposition was 95.0 wt % (82.4 vol %). The characteristics of thethermally conductive silicone rubber composition and thermallyconductive silicone rubber were measured as follows and the results werelisted in Table 4.

Practical Example 13

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 12 except for using an identical amountof dimethylpolysiloxane having one of the terminal ends of its molecularchain blocked by a trimethoxysiloxy group, represented by the formula:

instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 12. The consistency of the silicone rubber base wasmeasured in the same manner as in Practical Example 9 and the resultswere listed in Table 4.

Next, a thermally conductive silicone rubber composition was prepared bymixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt % (an amount sufficient to provide 10 ppm ofplatinum metal relative to the above-mentioned dimethylpolysiloxanehaving both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups). The content of alumina powder in thecomposition was 95.0 wt % (82.4 vol %). The characteristics of thethermally conductive silicone rubber composition and thermallyconductive silicone rubber were measured in the same manner as inPractical Example 9 and the results were listed in Table 4.

Practical Example 14

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 12 except for using an identical amountof dimethylpolysiloxane having one of the terminal ends of its molecularchain blocked by a trirethoxysiloxy group, represented by the formula:

instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 12. The consistency of the silicone rubber base wasmeasured in the same manner as in Practical Example 9 and the resultswere listed in Table 4.

Next, a thermally conductive silicone rubber composition was prepared bymixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt % (an amount sufficient to provide 10 ppm ofplatinum metal relative to the above-mentioned dimethylpolysiloxanehaving both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups). The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured in the same manner as in Practical Example 9 andthe results were listed in Table 4.

Comparative Example 14

An attempt was made to prepare a thermally conductive silicone rubberbase in the same manner as in Practical Example 12 except for using anidentical amount of dimethylpolysiloxane having one of the terminal endsof its molecular chain blocked by a trimethoxysiloxy group, representedby the formula:

instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 12, but an excessive increase in the viscosity of thebase made it impossible to add all of the 1,500 parts by weight of thetrue spherical alumina powder with an average particle size of 10 μm andthe 1,000 parts by weight of the irregular-shaped alumina powder with anaverage particle size of 2.2 μm.

Comparative Example 15

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 12 except for using an identical amountof dimethylpolysiloxane having one of the terminal ends of its molecularchain blocked by a trimethoxysiloxy group, represented by the formula:

instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 12. The consistency of the silicone rubber base wasmeasured in the same manner as in Practical Example 9 and the resultswere listed in Table 4.

Next, a thermally conductive silicone rubber composition was prepared bymixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt % (an amount sufficient to provide 10 ppm ofplatinum metal relative to the above-mentioned dimethylpolysiloxanehaving both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups). The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured in the same manner as in Practical Example 9 andthe results were listed in Table 4.

Comparative Example 16

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 12 except for using an identical amountof dimethylpolysiloxane having one of the terminal ends of its molecularchain blocked by a tiimethoxysiloxy group, represented by the formula:

instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 12. The consistency of the silicone rubber base wasmeasured in the same manner as in Practical Example 9 and the resultswere listed in Table 4.

Next, a thermally conductive silicone rubber composition was prepared bymixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt % (an amount sufficient to provide 10 ppm ofplatinum metal relative to the above-mentioned dimethylpolysiloxanehaving both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups). The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured in the same manner as in Practical Example 9 andthe results were listed in Table 4.

Comparative Example 17

A thermally conductive silicone rubber base was prepared in the samemanner as in Practical Example 12 except for using an identical amountof dimethylpolysiloxane having one of the terminal ends of its molecularchain blocked by a trimethoxysiloxy group, represented by the formula:

instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 12. The consistency of the silicone rubber base wasmeasured in the same manner as in Practical Example 9 and the resultswere listed in Table 4.

Next, a thermally conductive silicone rubber composition was prepared bymixing the silicone rubber base with 0.2 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt % (an amount sufficient to provide 10 ppm ofplatinum metal relative to the above-mentioned dimethylpolysiloxanehaving both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups). The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured in the same manner as in Practical Example 9 andthe results were listed in Table 4.

Comparative Example 18

An attempt was made to prepare a thermally conductive silicone rubberbase in the same manner as in Practical Example 12 except for using anidentical amount of dimethylpolysiloxane having both terminal ends ofits molecular chain blocked by trimethoxysiloxy groups, represented bythe formula:

instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 12, but an excessive increase in the viscosity of thebase made it impossible to add all of the 1,500 parts by weight of thetrue spherical alumina powder with an average particle size of 10 μm andthe 1,000 parts by weight of the irregular-shaped alumina powder with anaverage particle size of 2.2 μm.

Comparative Example 19

An attempt was made to prepare a thermally conductive silicone rubberbase in the same manner as in Practical Example 12 except for using anidentical amount of dimethylpolysiloxane having both terminal ends ofits molecular chain blocked by trimethoxysiloxy groups, represented bythe formula:

instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 12, but an excessive increase in the viscosity of thebase made it impossible to add all of the 1,500 parts by weight of thetrue spherical alumina powder with an average particle size of 10 μm andthe 1,000 parts by weight of the irregular-shaped alumina powder with anaverage particle size of 2.2 μm.

TABLE 4 Examples Practical Comparative Examples Examples Parameters 1213 14 15 16 17 Consistency 70 67 60 11 22 44 (mm/10) Moldability ◯ ◯ ◯ ΔΔ ◯ Thermal Conductivity 5.4 5.5 5.5 5.7 5.7 5.5 (W/m · k) Hardness 4043 46 88 74 60

The thermally conductive silicone rubber compositions listed in Table 4had extremely high alumina powder loading levels of 82.4 vol %.Comparison between Practical Examples 12 through 14 and ComparativeExamples 15 through 17 showed that depending on the number ofdimethylsiloxane repeat units in the dimethylpolysiloxanes having one ofthe terminal ends of their molecular chains blocked by trimethoxysiloxygroups, there was considerable variation in the consistency of thethermally conductive silicone rubber compositions, and, in addition,considerable variation in the hardness of the silicone rubbers obtainedby curing them. Additionally, comparison between Practical Example 12and Comparative Example 19 showed that even if the number ofdimethylsiloxane repeat units in the dimethylpolysiloxanes was the same,the consistency of the thermally conductive silicone rubber compositiongreatly varied, and, in addition, there was considerable variation inthe hardness of the silicone rubber produced by curing the compositionsdepending on whether the molecular chain was blocked with atrimethoxysiloxy group at one terminal end or with trimethoxysiloxygroups at both terminal ends. Furthermore, comparison betweenComparative Example 18 and Comparative Example 19 showed that, at equalnumber of dimethylsiloxane repeat units in the dimethylpolysiloxanes,the consistency of the thermally conductive silicone rubber compositionincreased and its handleability decreased regardless of the number ofdimethylsiloxane repeat units when both terminal ends of the molecularchain of the dimethylpolysiloxane were blocked by trimethoxysiloxygroups

Practical Example 15

Dimethylpolysiloxane (86.8 parts by weight) with a viscosity of 400mPa·s having both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups (vinyl group content=0.44 wt %), 900 parts byweight of spherical alumina powder with an average particle size of 10μm, and 10 parts by weight of organosiloxane represented by the formula:H(CH₃)₂SiO{(CH₃)₂SiO}₂₅Si(OCH₃)₃were combined in a mixer. Next, 2.2 parts by weight ofdimethylsiloxane-methylhydrogensiloxane copolymer having both terminalends of its molecular chain blocked by trimethylsiloxy groups, aviscosity of 5 mPa·s and an average of five silicon-bonded hydrogenatoms per molecule (content of silicon-bonded hydrogen atoms=0.74 wt %)and 0.5 parts by weight of 1-ethynyl-1-cyclohexanol as a cure reactioninhibitor were combined with the mixture. Finally, a thermallyconductive silicone rubber composition was prepared by combining themixture with 0.5 parts by weight of a1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum with aplatinum content of 0.5 wt %.

The characteristics of the thermally conductive silicone rubbercomposition and thermally conductive silicone rubber were determined asfollows, with the results listed in Table 5.

Consistency Of Thermally Conductive Silicone Rubber Composition

The ¼ cone penetration consistency of the thermally conductive siliconerubber composition was measured in accordance with the method stipulatedin JIS K 2220. A high consistency value was interpreted as evidence ofthe high plasticity and superior handleability of the thermallyconductive silicone rubber composition.

Moldability Of Thermally Conductive Silicone Rubber Composition

A layer of the thermally conductive silicone rubber composition with athickness of 2 mm was produced by sandwiching it between pieces ofethylene tetrafluoride resin film with a thickness of 0.2 mm, afterwhich it was cured by heating at 150° C. for 15 minutes. After that, theethylene tetrafluoride resin film was peeled off and visual examinationwas carried out to determine whether a silicone rubber sheet had beenformed. When a uniform silicone rubber sheet was formed, the moldabilityof the composition was evaluated as “excellent” and designated “∘”; whena sheet was formed, but had locations of partially low strength, themoldability was evaluated as “somewhat good” and designated as “Δ”; andwhen a sheet could not be formed, or had low strength when formed, themoldability was evaluated as “no good” and designated as “x”.

Thermal Conductivity Of Thermally Conductive Silicone Rubber

The thermal conductivity of the thermally conductiye silicone rubberobtained by heating the thermally conductive silicone rubber compositionat 150° C. for 15 minutes was determined in accordance with the hot wiremethod stipulated in JIS R 2616 using a Ouick Thermal ConductivityMeter, the QTM-500, manufactured by Kyoto Electronics Manufacturing Co.,Ltd.

Adhesive Strength Of Thermally Conductive Silicone Rubber

The thermally conductive silicone rubber composition was sandwichedbetween two pieces of identical material and then cured by heating at150° C. for 30 minutes. Aluminum plates (JIS H 4000, A1050P), nickelplates (SPCC-SB, and stainless steel plates (SUS-304 2B from Paltek Co.,Ltd. were used as the adherend, material. In addition, the surface areaof the plates, to which the composition was adhered, was 25 mm×10 mm,and the thickness of the adhered layer was 1 mm. The tensile shearadhesive strength of the thermally conductive silicone rubber wasmeasured in accordance with JIS K 6249.

TABLE 5 Example Practical Parameters Example 15 Consistency (mm/10) 109Moldability ◯ Thermal conductivity 3.0 (W/mK) Adhesive strength (N/cm²)Aluminum plates 193 Nickel plates 207 Stainless steel plates 161

Practical Example 16

A thermally conductive silicone grease was prepared by mixing 75 partsby weight of dimethylpolysiloxane with a viscosity of 300 mPa·s havingboth terminal ends of its molecular chain blocked by timethylsiloxygroups, 137 parts by weight of spherical alumina powder with an averageparticle size of 0.4 μm, 167 parts by weight of spherical alumina powderwith an average particle size of 2 μm, 616 parts by weight of sphericalalumina powder with an average particle size of 18 μm, and 5 parts byweight of dimethylpolysiloxane having one of the terminal ends of itsmolecular chain blocked by a trimethoxysiloxy group, represented by theformula:

in a mixer at room temperature.

Some of the thermally conductive silicone grease was placed in a 50-mlglass beaker and the ¼ cone penetration consistency of the siliconegrease was measured in accordance with the method stipulated in JIS K2220, with the results listed in Table 6. A high consistency value wasinterpreted as evidence of the high plasticity and superiorhandleability of the thermally conductive silicone grease. In addition,the thermally conductive silicone grease was wrapped in vinylidenechloride film and its thermal conductivity was determined in accordancewith the hot wire method stipulated in JIS R 2616 using a Quick ThermalConductivity Meter, the QTM-500, manufactured by Kyoto ElectronicsManufacturing Co., Ltd., with the results listed in Table 6.

Practical Example 17

A thermally conductive silicone grease was prepared in the same manneras in Practical Example 16 except for using an identical amount oforganosiloxane represented by the formula:(CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₂₉Si(OCH₃)₃instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 16. The consistency and thermal conductivity of thethermally conductive silicone grease were determined in the same manneras in Practical Example 16 and the results were listed in Table 6.

Practical Example 18

A thermally conductive silicone grease was prepared in the same manneras in Practical Example 16 except for using an identical amount ofoligosiloxane represented by the formula:H(CH₃)₂SiO{(CH₃)₂SiO}₂₅Si(OCH₃)₃instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 16. The consistency and thermal conductivity of thethermally conductive silicone grease were determined in the same manneras in Practical Example 16 and the results were listed in Table 6.

Practical Example 19

A thermally conductive silicone grease was prepared in the same manneras in Practical Example 16 except for using an identical amount ofoligosiloxane represented by the formula:(CH₃)₃SiO{(CH₂═CH)CH₃SiO}₃{(CH₃)₂SiO}₂₂Si(OCH₃)₃instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxysiloxy group that was used inPractical Example 16. The consistency and thermal conductivity of thethermally conductive silicone grease were determined in the same manneras in Practical Example 16 and the results were listed in Table 6.

Practical Example 20

A thermally conductive silicone grease was prepared in the same manneras in Practical Example 16 except for using an identical amount ofdimethylpolysiloxane with a viscosity of 400 mPa·s having both terminalends of its molecular chain blocked by dimethylvinylsiloxy groups (vinylgroup content=0.44 wt %) instead of the dimethylpolysiloxane with aviscosity of 300 mPa·s having both terminal ends of its molecular chainblocked by trimethylsiloxy groups that was used in Practical Example 16.The consistency and thermal conductivity of the thermally conductivesilicone grease were determined in the same manner as in PracticalExample 16 and the results were listed in Table 6.

Practical Example 21

A thermally conductive silicone grease was prepared in the same manneras in Practical Example 16 except for using an identical amount oforganosiloxane copolymer with a viscosity of 500 mPa·s consisting of2.22 mol % of siloxane units represented by the formula (CH₃)₃SiO_(1/2), 0.9 mol % of siloxane units represented by the formula (CH₃)₂(CH₂═CH)SiO_(1/2), 3.28 mol % of siloxane units represented by theformula CH₃ SiO_(3/2), and 93.6 mol % of siloxane units represented bythe formula (CH₃)₂ SiO_(2/2) instead of the dimethylpolysiloxane with aviscosity of 300 mPa·s having both terminal ends of its molecular chainblocked by trimethylsiloxy groups that was used in Practical Example 16.The consistency and thermal conductivity of the thermally conductivesilicone grease were determined in the same manner as in PracticalExample 16 and the results were listed in Table 6.

Comparative Example 20

An attempt was made to prepare a thermally conductive silicone grease inthe same manner as in Practical Example 16 except for using an identicalamount of methyltrimethoxysilane instead of the dimethylpolysiloxanehaving one of the terminal ends of its molecular chain blocked by atrimethoxylsiloxy group that was used in Practical Example 16, but anexcessive increase in the viscosity of the composition made itimpossible to add the specified amount of alumina powder and todetermine the consistency and measure the thermal conductivity of thethermally conductive silicone grease.

Comparative Example 21

An attempt was made to prepare a thermally conductive silicone grease inthe same manner as in Practical Example 16 except for using an identicalamount of oligosiloxane represented by the formula:(CH₃)₃SiO{(CH₃)₂SiO}₃Si(OCH₃)₃instead of the dimethylpolysiloxane having one of the terminal ends ofits molecular chain blocked by a trimethoxylsiloxy group that was usedin Practical Example 16, but an excessive increase in the viscosity ofthe composition made it impossible to add the specified amount ofalumina powder and to determine the consistency and thermal conductivityof the thermally conductive silicone grease.

Comparative Example 22

A thermally conductive silicone grease was prepared in the same manneras in Practical Example 16 except for using an identical amount ofdecyltrimethoxysilane instead of the dimethylpolysiloxane having one ofthe terminal ends of its molecular chain blocked by a trmethoxylsiloxygroup that was used in Practical Example 16. The consistency and thermalconductivity of the thermally conductive silicone grease were determinedin the same manner as in Practical Example 16 and the results werelisted in Table 6.

Comparative Example 23

A thermally conductive silicone grease was prepared in the same manneras in Practical Example 21 except for using an identical amount ofdecyltrimethoxysilane instead of the dimethylpolysiloxane having one ofthe terminal ends of its molecular chain blocked by a trmethoxylsiloxygroup that was used in Practical Example 21. The consistency and thermalconductivity of the silicone grease were determined in the same manneras in Practical Example 16 and the results were listed in Table 6.

TABLE 6 Examples Comparative Practical Examples Examples Parameters 1617 18 19 20 21 22 23 Consistency 120 83 82 92 115 90 66 67 (mm/10)Thermal 4.5 4.5 4.5 4.5 4.5 4.5 4.5 4.5 conductivity (W/m · k)

Practical Example 22

A thermally conductive silicone grease was prepared by mixing 74.5 partsby weight of dimethylpolysiloxane with a viscosity of 300 mPa·s havingboth terminal ends of its molecular chain blocked by trimethylsiloxygroups, 137 parts by weight of spherical alumina powder with an averageparticle size of 0.4 pn, 167.6 parts by weight of spherical aluminapowder with an average particle size of 2 μm, 615.4 parts by weight ofspherical alumina powder with an average particle size of 18 μm, and 5.0parts by weight of organopolysiloxane represented by the formula:{(CH₃)₃SiO{(CH₃)₂SiO}₁₁₀}Si(OCH₃)₃and 0.5 parts by weight of methyltrimethoxysilane under heating andreduced pressure in a Ross mixer for 1 hour at 150° C., cooling themixture to room temperature, and continuing agitation for another hour.The initial consistency of the thermally conductive silicone grease andits consistency after conducting heat treatment for 24 hours at 105° C.were determined in the same manner as in Practical Example 16 and theresults were listed in Table 7. In addition, the thermal conductivity ofthe thermally conductive silicone grease was determined in the samemanner as in Practical Example 16 and the results were listed in Table7.

Practical Example 23

A thermally conductive silicone grease was prepared by mixing 72.05parts by weight of dimethylpolysiloxane with a viscosity of 300 mPa·shaving both terminal ends of its molecular chain blocked bytrimethylsiloxy groups, 137 parts by weight of spherical alumina powderwith an average particle size of 0.4 μm, 167.6 parts by weight ofspherical alumina powder with an average particle size of 2 μm, 615.4parts by weight of spherical alumina powder with an average particlesize of 18 μm, 7.5 parts by weight of organopolysiloxane represented bythe formula:{(CH₃)₃SiO{(CH₃)₂SiO}₁₁₀}Si(OCH₃)₃and 0.45 parts by weight of methyltrimethoxysilane under heating andreduced pressure in a Ross mixer for 1 hour at 150° C., cooling themixture to room temperature, and continuing agitation for another hour.The consistency and thermal conductivity of the thermally conductivesilicone grease were determined in the same manner as in PracticalExample 16 and the results were listed in Table 7.

Practical Example 24

A thermally conductive silicone grease was prepared by mixing 75 partsby weight of dimethylpolysiloxane with a viscosity of 300 mPa·s havingboth terminal ends of its molecular chain blocked by trimethylsiloxygroups, 137 parts by weight of spherical alumina powder with an averageparticle size of 0.4 μm, 167.6 parts by weight of spherical aluminapowder with an average particle size of 2 μm, 615.4 parts by weight ofspherical alumina powder with an average particle size of 18 μm, and 5.0parts by weight of organopolysiloxane represented by the formula:{(CH₃)₃SiO{(CH₃)₂SiO}₁₁₀}Si(OCH₃)₃under heating and reduced pressure in a Ross mixer for 1 hour at 150°C., cooling the mixture to room temperature, and continuing agitationfor another hour. The consistency and thermal conductivity of thethermally conductive silicone grease were determined in the same manneras in Practical Example 16 and the results were listed in Table 7.

TABLE 7 Examples Practical Examples Parameters 22 23 24 ConsistencyInitial 112 97 96 (mm/10) After 24 hours at 105° C. 96 97 65 Thermalconductivity (W/m · k) 4.3 4.3 4.1

Practical Example 25

Dimethylpolysiloxane (43.6 parts by weight)with a viscosity of 400mPa·shaving both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups (vinyl group content=0.44 wt %), 552 parts byweight of spherical alumina powder with an average particle size of 40μm, 368 parts by weight of irregular-shaped alumina powder with anaverage particle size of 2.2 μm, 15 parts by weight of organosiloxanerepresented by the formula:{(CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₂₉}Si(OCH₃)₃and 15 parts by weight of organosiloxane represented by the formula:(CH₃)₃SiO{(CH₃)₂SiO}₁₁₀Si(OCH₃)₃were combined in a mixer. Next, 3.4 parts by weight ofdimethylsiloxane-methylhydrogensiloxane copolymer having both terminalends of its molecular chain blocked by trimethylsiloxy groups, aviscosity of 5 mPa·s, and an average of five silicon-bonded hydrogenatoms per molecule (content of silicon-bonded hydrogen atoms=0.74 wt %),0.5 parts by weight of 1-ethynyl-1-cyclohexanol as a cure reactioninhibitor, and 1.0 part by weight of 3-glycidoxypropyltrimethoxysilaneand 1.0 part by weight of dimethylsiloxane-methylvinylsiloxane copolymerhaving both terminal ends of its molecular chain blocked byhydroxydimethyl groups and an average of two silicon-bonded vinyl groupsper molecule (vinyl group content=9.6 wt %) as an adhesion promoter werecombined with the mixture. Finally, a thermally conductive siliconerubber composition was prepared by combining the mixture with 0.5 partsby weight of a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex ofplatinum with a platinum content of 0.5 wt %. The characteristics of thethermally conductive silicone rubber composition and thermallyconductive silicone rubber were determined in the same manner as inPractical Example 1 and the results were listed in Table 8.

Practical Example 26

Dimethylpolysiloxane (42.9 parts by weight) with a viscosity of 400mPa·s having both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups (vinyl group content=0.44 wt %), 552 parts byweight of spherical alumina powder with an average particle size of 40μm, 368 parts by weight of irregular-shaped alumina powder with anaverage particle size of 2.2 μm, 24 parts by weight of organosiloxanerepresented by the formula:{(CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₂₉}Si(OCH₃)₃and 6 parts by weight of organosiloxane represented by the formula:(CH₃)₃SiO{(CH₃)₂SiO}₁₁₀Si(OCH₃)₃were combined in a mixer. Next, 4.1 parts by weight ofdimethylsiloxane-methylhydrogensiloxane copolymer having both terminalends of its molecular chain blocked by trimethylsiloxy groups, aviscosity of 5 mPa·s, and an average of five silicon-bonded hydrogenatoms per molecule (content of silicon-bonded hydrogen atoms=0.74 wt %),0.5 parts by weight of 1-ethynyl-1-cyclohexanol as a cure reactioninhibitor, and 1.0 part by weight of 3-glycidoxypropyltrimethoxysilaneand 1.0 part by weight of dimethylsiloxane-methylvinylsiloxane copolymerhaving both terminal ends of its molecular chain blocked byhydroxydimethyl groups and an average of two silicon-bonded vinyl groupsper molecule (vinyl group content=9.6 wt %) as an adhesion promoter werecombined with the mixture. Finally, a thermally conductive siliconerubber composition was prepared by combining the mixture with 0.5 partsby weight of a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex ofplatinum with a platinum content of 0.5 wt %. The characteristics of thethermally conductive silicone rubber composition and thermallyconductive silicone rubber were determined in the same manner as inPractical Example 1 and the results were listed in Table 8.

Practical Example 27

Dimethylpolysiloxane (44.0 parts by weight) with a viscosity of 400mPa·s having both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups (vinyl group content=0.44 wt %), 552 parts byweight of spherical alumina powder with an average particle size of 40μm, 368 parts by weight of irregular-shaped alumina powder with anaverage particle size of 2.2 μm, 10 parts by weight of organosiloxanerepresented by the formula:{(CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₂₉}Si(OCH₃)₃and 20 parts by weight of organosiloxane represented by the formula:(CH₃)₃SiO{(CH₃)₂SiO}₁₁₀Si(OCH₃)₃were combined in a mixer. Next, 3.0 parts by weight ofdimethylsiloxane-methylhydrogensiloxane copolymer having both terminalends of its molecular chain blocked by trimethylsiloxy groups, aviscosity of 5 mPa·s, and an average of five silicon-bonded hydrogenatoms per molecule (content of silicon-bonded hydrogen atoms=0.74 wt %),0.5 parts by weight of 1-ethynyl-1-cyclohexanol as a cure reactioninhibitor, and 1.0 part by weight of 3-glycidoxypropyltrimethoxysilaneand 1.0 part by weight of dimethylsiloxane-methylvinylsiloxane copolymerhaving both terminal ends of its molecular chain blocked byhydroxydimethyl groups and an average of two silicon-bonded vinyl groupsper molecule (vinyl group content=9.6 wt %) as an adhesion promoter werecombined with the mixture. Finally, a thermally conductive siliconerubber composition was prepared by combining the mixture with 0.5 partsby weight of a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex ofplatinum with a platinum content of 0.5 wt %. The characteristics of thethermally conductive silicone rubber composition and thermallyconductive silicone rubber were determined in the same manner as inPractical Example 1 and the results were listed in Table 8.

Practical Example 28

Dimethylpolysiloxane (43.2 parts by weight) with a viscosity of 400mPa·s having both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups (vinyl group content=0.44 wt %), 552 parts byweight of spherical alumina powder with an average particle size of 40μm, 368 parts by weight of irregular-shaped alumina powder with anaverage particle size of 2.2 μm, 20 parts by weight of organosiloxanerepresented by the formula:{(CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₂₉}Si(OCH₃)₃and 10 parts by weight of organosiloxane represented by the formula:(CH₃)₃SiO{(CH₃)₂SiO}₁₁₀Si(OCH₃)₃were combined in a mixer. Next, 3.8 parts by weight ofdimethylsiloxane-methylhydrogensiloxane copolymer having both terminalends of its molecular chain blocked by trimethylsiloxy groups, aviscosity of 5 mPa·s, and an average of five silicon-bonded hydrogenatoms per molecule (content of silicon-bonded hydrogen atoms=0.74 wt %),0.5 parts by weight of 1-ethynyl-1-cyclohexanol as a cure reactioninhibitor, and 1.0 part by weight of 3-glycidoxypropyltrimethoxysilaneand 1.0 part by weight of dimethylsiloxane-methylvinylsiloxane copolymerhaving both terminal ends of its molecular chain blocked byhydroxydimethyl groups and an average of two silicon-bonded vinyl groupsper molecule (vinyl group content=9.6 wt %) as an adhesion promoter werecombined with the mixture. Finally, a thermally conductive siliconerubber composition was prepared by combining the mixture with 0.5 partsby weight of a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex ofplatinum with a platinum content of 0.5 wt %. The characteristics of thethermally conductive silicone rubber composition and thermallyconductive silicone rubber were determined in the same manner as inPractical Example 1 and the results were listed in Table 8.

Comparative Example 24

Dimethylpolysiloxane (85.4 parts by weight) with a viscosity of 400mPa·s having both terminal ends of its molecular chain blocked bydimethylvinylsiloxy groups (vinyl group content=0.44 wt %), 900 parts byweight of spherical alumina powder with an average particle size of 10μm, and 10 parts by weight of methyltrimethoxysilane were combined in amixer. Next, 3.6 parts by weight ofdimethylsiloxanemethylhydrogen-siloxane copolymer having both terminalends of its molecular chain blocked by trimethylsiloxy groups, aviscosity of 5 mPa·s, and an average of five silicon-bonded hydrogenatoms per molecule (content of silicon-bonded hydrogen atoms=0.74 wt %),0.5 parts by weight of 1-ethynyl-1-cyclohexanol as a cure reactioninhibitor, and 1.0 part by weight of 3-glycidoxypropyltrimethoxysilaneand 1.0 part by weight of dimethylsiloxane-methylvinylsiloxane copolymerhaving both terminal ends of its molecular chain blocked byhydroxydimethyl groups and an average of two silicon-bonded vinyl groupsper molecule (vinyl group content=9.6 wt %) as an adhesion promoter werecombined with the miuture. Finally, a thermally conductive siliconerubber composition was prepared by combining the mixture with 0.5 partsby weight of a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex ofplatinum with a platinum content of 0.5 wt %. The characteristics of thethermally conductive silicone rubber composition and thermallyconductive silicone rubber were determined in the same manner as inPractical Example 1 and the results were listed in Table 8.

Comparative Example 25

A thermally conductive silicone rubber composition was prepared in thesame manner as in Comparative Example 24 except for using an identicalamount of decyltrimethoxysilane instead of methyltrimethoxysilane. Thecharacteristics of the thermally conductive silicone rubber compositionand thermally conductive silicone rubber were determined in the samemanner as in Practical Example 1 and the results were listed in Table 8.

Comparative Example 26

A thermally conductive silicone rubber composition was prepared in thesame manner as in Comparative Example 24 except for using an identicalamount of organosiloxane represented by the formula:(CH₃)₃SiO{(CH₃)₂SiO}₅₀Si(OCH₃)₃instead of methyltrimethoxysilane. The characteristics of the thermallyconductive silicone rubber composition and thermally conductive siliconerubber were determined in the same manner as in Practical Example 1 andthe results were listed in Table 8.

TABLE 8 Examples Comparative Practical Examples Examples Parameters 2526 27 28 24 25 26 Consistency (mm/10) 148 121 144 136 30 103 123Moldability ◯ ◯ ◯ ◯ X X X Thermal conductivity 4.3 4.3 4.3 4.3 3.0 3.03.0 (W/m · k) Adhesive strength 257 296 203 299 212 54 13 (N/cm²)

Practical Example 29

A thermally conductive silicone grease was prepared by mixing 70 partsby weight of dimethylpolysiloxane with a viscosity of 300 mPa·s havingboth terminal ends of its molecular chain blocked by trimethylsiloxygroups, 552 parts by weight of spherical alumina powder with an averageparticle size of 40 μm, 368 parts by weight of irregular-shaped aluminapowder with an average particle size of 2.2 μm, 5.0 parts by weight oforganosiloxane represented by the formula:{(CH₂═CH)(CH₃)₂SiO{(CH₃)₂SiO}₂₉}Si(OCH₃)₃and 5.0 parts by weight of organosiloxane represented by the formula:(CH₃)₃SiO{(CH₃)₂SiO}₁₁₀Si(OCH₃)₃at room temperature.

Some of the thermally conductive silicone grease was placed in a 50-mlglass beaker and the ¼ cone penetration consistency of the siliconegrease was measured in accordance with the method stipulated in JIS K2220, with the results listed in Table 9. Also, a high consistency valuewas interpreted as evidence of the high plasticity and superiorhandleability of the thermally conductive silicone grease. In addition,the thermally conductive silicone grease was wrapped in vinylidenechloride film and its thermal conductivity was determined in accordancewith the hot wire method stipulated in JIS R 2616 using a Quick ThermalConductivity Meter, the QTM-500, manufactured by Kyoto ElectronicsManufacturing Co., Ltd., with the results listed in Table 9.

Practical Example 30

A thermally conductive silicone grease was prepared by mixing 70 partsby weight of dimethylpolysiloxane with a viscosity of 300 mPa·shavingboth terminal ends of its molecular chain blocked by trimethylsiloxygroups, 552 parts by weight of spherical alumina powder with an averageparticle size of 40 μm, 368 parts by weight of irtegular-shaped aluminapowder with an average particle size of 2.2 μm, and 10 parts by weightof organosiloxane represented by the formula:(CH₃)₃SiO{(CH₃)₂SiO}₁₁₀Si(OCH₃)₃at room temperature. The characteristics of the thermally conductivesilicone grease were determined in the same manner as in PracticalExample 29 and the results were listed in Table 9.

TABLE 9 Examples Practical Examples Parameters 29 30 Consistency (mm/10)112 89 Thermal conductivity 4.3 4.3 (W/m · k)

INDUSTRIAL APPLICABILITY

The thermally conductive silicone composition of the present inventionis characterized by exhibiting excellent handleability despitecontaining large quanitities of thermally conductive fillers added inorder to produce a silicone composition exhibiting high thermalconductivity.

1. A thermally conductive silicone composition comprising: (A) anorganopolysiloxane, (B) a thermally conductive filler comprising a metalpowder, a metal oxide powder, a metal nitride powder, a metal carbidepowder, a soft magnetic alloy powder, a ferrite, and combinationsthereof, and (C) at least one organosiloxane selected from the groupconsisting of (i) an organosiloxane represented by the general formula:[R¹ _(a)R² _((3−a))SiO(R¹ _(b)R² _((2−b))SiO)_(m)(R² ₂SiO)_(n)]_(c)SiR²_([4−(c+d)])(OR³)_(d)  where R¹ stand for monovalent hydrocarbon groupshaving aliphatic unsaturated bonds, R² stand for identical or differentmonovalent hydrocarbon groups having no aliphatic unsaturated bonds, R³is selected from a group consisting of an alkyl, alkoxyalkyl, alkenyl,and acyl, the subscript a is an integer of 0 to 3, b is 1 or 2, c is aninteger of 1 to 3, d is an integer of 1 to 3, c+d is an integer of 2 to4, m is an integer of 0 or greater, and n is integer of from 10 to 100,with the proviso that m is an integer of 1 or greater when a is 0, (iii)an organosiloxane represented by the general formula:

 where R⁴ is identical or different monovalent hydrocarbon groups, R⁵ isan oxygen atom or divalent hydrocarbon group, R³ is the same as definedabove, p is an integer of 105 to 200, and d is the same as above, and(iv) an organosiloxane represented by the general formula:[H_(e)R² _((3−e))SiO(R² ₂SiO)_(n)]_(c)SiR² _([4−(c+d)])(0R³)_(d)  whereR², R³, c,d and n are the same as defined above, and e is an integer of1 to
 3. 2. The thermally conductive silicone composition according toclaim 1, in which the average particle size of Component (B) is 0.1 to100 μm.
 3. The thermally conductive silicone composition according toclaim 1, in which Component (B) is an alumina powder.
 4. The thermallyconductive silicone composition according to claim 3, in which Component(B) is a mixture of (B₁) a spherical alumina powder with an averageparticle size of greater than 5 to 50 μm and (B₂) a spherical orinegular-shaped alumina powder with an average particle size of 0.1 to 5μm.
 5. The thermally conductive silicone composition according to claim4, in which Component (B) is made up of 30 to 90 wt % of component (B₁)and 10 to 70 wt % of component (B₂).
 6. The thermally conductivesilicone composition according to claim 1, in which the content ofComponent (B) is 500 to 2,500 parts by weight per 100 parts by weight ofComponent (A).
 7. The thermally conductive silicone compositionaccording to claim 1, in which the content of Component (C) is 0.1 to 10parts by weight per 100 parts by weight of Component (B).
 8. Thethermally conductive silicone composition according to claim 1, in whichComponent (B) is surface-treated with Component (C) in Component (A). 9.The thermally conductive silicone composition according to claim 1, inwhich the thermally conductive silicone composition further contains (D)a curing agent and is curable.
 10. The thermally conductive siliconecomposition according to claim 9, in which the thermally conductivesilicone composition is curable by means selected from the groupconsisting of (i) a hydrosilation reaction, (ii) condensation reaction,and (iii) an organic peroxide-induced free radical reaction.
 11. Thethermally conductive silicone composition according to claim 9, in whichthe thermally conductive silicone composition is curable by means of ahydrosilation reaction.
 12. The thermally conductive siliconecomposition according to claim 1, in which Component (A) has a viscosityof from 100 to 50,000 MPa·s at 25°0 C.
 13. The thermally conductivesilicone composition according to claim 12, in which Component (A)comprises at least one of an alkyl group, an alkenyl group, and an arylgroup.
 14. The thermally conductive silicone composition according toclaim 13, in which the alkyl group comprises a methyl group, the alkenylgroup comprises a vinyl group and the aryl group comprises a phenylgroup.
 15. The thermally conductive silicone composition according toclaim 14, in which Component (A) has an average of at least 0.8silicon-bonded alkyenyl groups per molecule.
 16. The thermallyconductive silicone composition according to claim 1, in which Component(A) has an average of at least 0.1 silicon-bonded alkyenyl groups permolecule.
 17. The thermally conductive silicone composition according toclaim 16, in which Component (A) has an average of at least 0.8silicon-bonded alkyenyl groups per molecule.
 18. The thermallyconductive silicone composition according to claim 1, in which p is aninteger of 110 to 190.